FL 6 - Chem/Phys

Question 1

Oxidation of aldehydes produces which functional group?

Answer 1

A strong oxidizing agent will likewise oxidize an aldehyde to a carboxylic acid.

Many of the stronger oxidizing agents such as KMnO₄will transform aldehydes into carboxylic acids.Tollens’ reagent [Ag(NH₃)₂]⁺ is one such oxidant. A shiny mirror of metallic silver is deposited through oxidation of aldehydes to form carboxylic acids by Tollens’ reagent, so it is a frequently used test for aldehydes in qualitative analysis

Question 2

When ketones are oxidized by Tollen’s reagent, what does the product look like?

Answer 2

Ketones are not oxidized by Tollens’ reagent, therefore no “product” is formed, so the treatment of a ketone with Tollens’ reagent in a glass test tube does not result in a silver mirror.

Question 3

A ______ ______ can be oxidized to an aldehyde by a mild oxidizing agent (such as PCC) or to a carboxylic acid by a strong oxidizing agent like NaCr₂O₇.

Answer 3

A primary alcohol can be oxidized to an aldehyde by a mild oxidizing agent (such as PCC) or to a carboxylic acid by a strong oxidizing agent like NaCr₂O₇.

Question 4

A ________ ______will be oxidized to a ketone by either a mild or a strong oxidizing agent.

Answer 4

A secondary alcohol will be oxidized to a ketone by either a mild or a strong oxidizing agent.

Question 5

When aldehydes are oxidized by Tollen’s reagent, what does the product look like?

Answer 5

Many of the stronger oxidizing agents such as KMnO₄will transform aldehydes into carboxylic acids.Tollens’ reagent [Ag(NH₃)₂]⁺ is one such oxidant. A shiny mirror of metallic silver is deposited through oxidation of aldehydes to form carboxylic acids by Tollens’ reagent, so it is a frequently used test for aldehydes in qualitative analysis

Question 6

A ______ reducing agent, such as LiAlH₄, can reduce a carboxylic acid directly to an alcohol.

Answer 6

A strong reducing agent, such as LiAlH₄, can reduce a carboxylic acid directly to an alcohol.

Question 7

Will NaBH₄ reduce a carboxylic acid? Why/Why not?

Answer 7

A weak reducing agent, such as NaBH₄ will not reduce carboxylic acids at all.

Question 8

What types of reducing agents can produce alcohols?

Answer 8

Both mild and strong reducing agents can reduce aldehydes and ketones to primary and secondary alcohols, respectively.

Question 9

What types of oxidizing agents + substrates can produce a ketone?

Answer 9

A secondary alcohol will be oxidized to a ketone by either a mild or a strong oxidizing agent.

Question 10

An ____ configuration involves two groups immediately adjacent to each other, while _____ structures have two substituents separated by a single carbon. Finally, ____ diols include two –OH groups immediately across from each other on the ring.

Answer 10

An ortho configuration involves two groups immediately adjacent to each other, while meta structures have two substituents separated by a single carbon. Finally, para diols include two –OH groups immediately across from each other on the ring.

Question 11

All carboxylic acid derivatives are formed through a ________ ________ reaction, and upon hydrolysis, they all _____________

Answer 11

All carboxylic acid derivatives are formed through a nucleophilic substitution reaction, and upon hydrolysis, they all convert back to their parent carboxylic acid.

Question 12

_____________ are formed when carboxylic acids react with thionyl chloride (SOCl₂), PCl₃, or PCl₅. They are the ______ reactive derivatives of carboxylic acid.

Answer 12

Acid chlorides are formed when carboxylic acids react with thionyl chloride (SOCl₂), PCl₃, or PCl₅. They are the most reactive derivatives of carboxylic acid.

Question 13

LiAlH₄ is a (strong/weak) base and a (strong/weak) reducing agent

Answer 13

LiAlH₄ is a strong base and a strong reducing agent

Question 14

What will happen to a molecule that has both a ketone and a carboxylic acid when reacted with LiAlH₃?

Answer 14

Both the ketone and the carboxylic acid will be reduced to alcohols. This is because LiAlH₃ is not chemoselective and is a strong reducing agent.

Question 15

What will happen to a molecule that has both a ketone and a carboxylic acid when reacted with BH₃?

Answer 15

Only the carboxylic acid will be reduced to an alcohol. This is because BH₃ is chemoselective.

Question 16

Why is it difficult to synthesize an amide directly from a carboxylic acid?

Answer 16

Amides are the most stable (least reactive) of the carboxylic acid derivatives because the amino substituent is a very poor leaving group. In order to synthesize amides however, one cannot simply use the amino substituent as a nucleophile; as a relatively strong base, it will instead preferentially participate in an acid-base neutralization reaction with the acidic hydrogen of the organic acid.

Instead, one must first create an acid chloride, or an acid anhydride, to eliminate the confounding acidic hydrogen. Afterwards, one can proceed with a normal nucleophilic substitution.

Question 17

In the conversion of a fatty acid to an ester, what functional groups are changed?

Answer 17

In the conversion of a fatty acid to an ester, we lose a hydroxyl group, and neither gain nor lose any other relevant functional groups.

This is the conversion of a carboxylic acid to an ester, in which the carboxylic acid -OH is replaced with an -OR.

Question 18

The hydrocarbon tails of trans fats stack _____ densely than those of comparable cis fats.

Answer 18

As shown in the image below, the hydrocarbon tails of trans fats are very similar to those of saturated fatty acids, meaning that they stack together more densely than the corresponding cis fats. The denser, more stable stacking of trans fats means that they are more likely to be solids—and therefore less likely to be liquids—at room temperature. This property of trans fats makes them useful for inclusion in commercially produced baked goods because the stable solid state of trans fats contributes to longer shelf life. Unfortunately, trans fats have also been closely associated with an elevated risk of cardiovascular disease.

Question 19

Will a -cis or a -trans fatty acid have a higher melting point?

Which is more likely to be a liquid at room temperature?

Answer 19

A -cis double bond in a fatty acid makes a kink, preventing stacking of multiple fatty acids, and significantly lowering the possible van der waals forces, lowering the melting point. Therefore, a -trans fatty acid, with its ability to stack, will have a higher melting point and will be more likely to be a solid at room temperature.

Question 20

In gas-liquid chromatography, what compounds will have the highest retention time?

Answer 20

In gas-liquid chromatography, the sample is volatilized in a hot chamber. The higher the boiling point temperature, the more time the compound will spend at the beginning of the chamber waiting to get volatilized. Retention time is the time it takes for the sample to reach the detector. Therefore, the compound with the highest boiling point will have the highest retention time.

Question 21

Reaction 1 releases 188.6 J, what is the ∆H of Reaction 2?

Answer 21

Reaction 2 is simply Reaction 1 run in reverse with the stoichiometric coefficients doubled. So when we’re told that Reaction 1 releases 188.6 J, that means its enthalpy change is -188.6 J. The reverse reaction would have an enthalpy change of +188.6 J, and if you double the stoichiometry, you must double this value to get +377.2 J.

Question 22

Define an Arrhenius base

Answer 22

An Arrhenius base is a compound or element that releases hydroxide ions into a solution when dissolved in water.

Question 23

Define a bronsted-Lowry base

Answer 23

The bronsted-Lowry base is a proton acceptor.

Question 24

Define a Bronsted-Lowry acid

Answer 24

A Bronsted-Lowry acid is a proton donor.

Question 25

Define a **Lewis Acid**

Answer 25

A **Lewis acid** is a lone electron pair acceptor.

Question 26

When a transition metal is ionized, are electrons removed from the following s subshell of from the subshell of the transition metal?

Answer 26

During the ionization of transition metals, electrons from 4*s* subshell orbitals are generally removed before those from 3*d* subshell orbitals. This is because it is generally true that, when occupied by electrons, electrons of 4*s* subshell orbitals are higher energy than those in 3*d* subshell orbitals.

Question 27

This technique detects conjugated pi systems and metal-to-ligand charge transfer species. The appearance of a peak corresponding to the charge transfer component will appear using this technique.

Answer 27

**UV-VIS spectroscopy.**

Question 28

KMnO₄ is a _____ \_\_\_\_\_ agent

Answer 28

KMnO₄ is a strong oxidizing agent. Often a reagent that is commonly used to oxidize alcohols to carboxylic acids.

Question 29

\_\_\_\_\_\_\_\_ is an insulin-regulated glucose transporter found primarily in adipose tissues and striated muscle (skeletal and cardiac).

Answer 29

**GLUT4** is an insulin-regulated glucose transporter found primarily in adipose tissues and striated muscle (skeletal and cardiac).

Question 30

When is positive beta decay most likely to occur?

Answer 30

Positive beta decay, also known as positron emission, **occurs when the proton-to-neutron ratio is too high.**

Question 31

How does the speed of a photon on the sun differ from the speed of a photon on earth?

Answer 31

**They would have identical speeds.** The speed of a photon is always the speed of light, no matter its energy.

Question 32

Describe **Laminar Flow**

Answer 32

Laminar flow is due to shear forces (friction) between the fluid and the solid surface of the tube. This results in layers having a gradient of velocities, in which the flow is the fastest in the middle of the tube (where friction is low) and slowest near the surface (where friction is high).

Question 33

What is a **chaotropic agent** and a common use of such?

Answer 33

A **chaotropic agent** is any molecule in an aqueous solution that can **disrupt the hydrogen bonding** network including the bonds between water molecules. As such, these agents (urea is one example) are capable of **denaturing** proteins by disrupting the hydrogen bonds that stabilize their configurations.

Question 34

What difference in effect is seen between ionizing radiation and non-ionizing radiation?

Answer 34

**Ionizing radiation**, as seen when irradiating proteins with X-rays or gamma rays can denature them because they break bonds. **Non-ionizing radiation** does **NOT** break bonds and therefore, **does not denature proteins.**

Question 35

Surface residues are **(more/less)** likely than residues found at protein core to be keystones for protein **structure**.

Answer 35

Surface residues are **less likely** to be “keystones” for the protein structure, as those sorts of residues tend to be found in the protein’s core. A helpful analogy is a modern skyscraper: the outside wall is often made of glass and steel, with a concrete core that serves as the main weight-bearing material. A surface residue that isn’t critical for structure may still be critical for the function of the protein and may be important for binding a substrate.

Question 36

There is **(more/less)** oxygen in the air at higher elevation.

Answer 36

There is **less** oxygen in the air at higher elevation.

Question 37

What physiological responses will be seen in the hematocrit of someone living at higher elevation?

Answer 37

A person living at a higher elevation will produce more red blood cells because there is less oxygen in the air. The kidney has receptors that read the oxygen levels in the blood and produce erythropoietin in order to produce more red blood cells. This will increase the hematocrit.

Question 38

Is Ammonia an acid or a base?

Answer 38

Ammonia is a **weak base**

Question 39

Can ketones be oxidized further? Why/why not?

Answer 39

No. Ketones are difficult to oxidize further because their C=O carbon already possesses two carbon-carbon bonds. C-C bonds cannot be broken easily, meaning that ketones cannot easily gain C-O bonds.

Question 40

Because pH affects the reaction, a student carefully creates a suitable aqueous solvent for the reaction. After bubbling CO₂ through the solution, he checks the pH and is surprised to find that it is not the same as the original value. What is the most likely cause for this?

Answer 40

The pH will be **more acidic** because CO₂ will combine with H₂O to create carbonic acid. The combination of CO₂ and H₂O to make carbonic acid (H₂CO₃) is a reaction that you must know for the MCAT. Carbonic acid and its conjugate base (bicarbonate) play a large role in maintaining the pH of the human body. While this reaction is sped up by carbonic anhydrase, it will still occur even in the absence of this enzyme, albeit at a slower rate.

Question 41

A horizontal force of 100 N is applied to a 50-kg box that is accelerating at 1 m/s² on a rough, horizontal surface. What is the work done by kinetic friction if the box is moved 4 m?

Answer 41

Question 42

Can CO₂ cause a decrease in pH when dissolved in water?

Answer 42

When carbon dioxide dissolves in water, it slowly establishes equilibrium between the dissolved carbon dioxide and carbonic acid (H₂CO₃), which is a weak acid that would lower the pH. Carbonic acid anhydrase speeds up this reaction in biological systems.

Question 43

If an object’s initial velocity is 100 m/s, and it accelerates at 20 m/s² for 20 seconds, how fast will it be going?

Answer 43

To solve this problem, we must plug the given values into the formula **v****_f****= v****_i** **+ at**. This yields: v_f = v_i + at v_f = 100 m/s + (20 m/s²)(20 s) = **500 m/s**

Question 44

If I am going 20 m/s and I accelerate at 4 m/s² for 10 seconds, how far will I travel?

Answer 44

To solve this problem, we need to plug the given values into the equation **d = v****_i****(t) + (1/2) at****²**. This yields: d = v_it + (1/2) at² d = (20 m/s )(10 s) + (1/2)(4 m/s²)(10 s)² d = 200 m + 200 m d = **400 m**

Question 45

What is the distance traveled by an object that starts at rest and accelerates at 10 m/s² for 6 seconds?

Answer 45

To solve this problem, we need to plug into the formula **d = v****_i****(t) + (1/2) at****²**. This yields: d = v_i(t) + (1/2) at² d = (0)(6 s) + (1/2) (10 m/s²)(6 s)² d = 0 + (1/2) (10)(36) d = **180 m**

Question 46

If an object starts at a velocity of 6 m/s and accelerates at 1 m/s², how fast would it be going after it traveled 32 meters?

Answer 46

To solve this problem, we must to remember to use the formula **v****_f²****= v****_i²** **+ 2ad**. Plugging in the given values yields: v_f² = v_i² + 2ad v_f² = (6 m/s)² + 2(1 m/s²)(32 m) v_f² = 36 + 64 = 100 v_f = **10 m/s**

Question 47

If a person drops a marble from the top of a building located 10 meters above the ground, how long will it take for the marble to reach the ground?

Answer 47

Using the kinematics equation, **d = v****_i****t + 0.5at****²**. Plugging in the given values (d = 10m, v_i = 0m/s, a = 10m/s²), we get **t = sqrt(2)** seconds, or approximately 1.4s.

Question 48

True or False: If a basketball is thrown up into the air, it will hit the ground at the same time that it would if it was simply dropped.

Answer 48

This statement is **false**. Throwing the ball horizontally and dropping the ball would both result in the ball hitting the ground at the same time. However, throwing the ball up into the air, as in this question, will cause it to take longer to come back down.

Question 49

If a cannonball is fired at 100 m/s at a 30 degree angle above the horizontal, what is the initial vertical velocity? (Note that cos 30 = 0.87 and sin 30 = 0.5.)

Answer 49

Because velocity in the y-direction is equal to sinθ times the total velocity, we can do the following calculations: **v****_y****= v****_i** **sinθ** v_y = (100 m/s) sin(30) v_y = **50 m/s**

Question 50

How long will it take for a ball to hit the ground if it is thrown vertically up in the air at a velocity of 50 m/s?

Answer 50

For the first half of the ball’s flight, the initial velocity will be 50 m/s and the final velocity will be equal to 0 m/s (as it reaches the peak of its flight). Acceleration will be g, and will be causing the ball to slow down, so we can use the value of -10 m/s². **v_f = v_i + at** (0)= (50) + (-10) t -50 = -10t t = 5 seconds. However, that is only the first half of the flight! The ball must come back down, which will take the same amount of time as it took to go up. **Thus, the total flight time will be 10 seconds.**

Question 51

A ball is thrown so that it has an initial horizontal velocity of 30 m/s and an initial vertical velocity of 6 m/s. If it is in the air for 6 seconds, how far will it land from its point of origin?

Answer 51

This question is much simpler than it looks. There is no force acting on the ball in the x-direction after it is thrown, so its velocity in the x-direction will not change. Since we know that the ball is in the air for 6 seconds, we can calculate the distance traveled by multiplying the horizontal velocity by time: **d = vt** = (30 m/s)(6 s) = **180 meters**

Question 52

If a dart is thrown at a speed of 40 m/s and an angle of 30 degrees, how far will it travel horizontally before it hits the ground? (Note that cos 30 = 0.87 and sin 30 = 0.5.)

Answer 52

In order to answer this question, we need to find: (1) the initial velocity in the y-direction, (2) the total time that the dart is in the air, and (3) the velocity in the x-direction. To calculate the initial velocity in the y-direction, we can multiply the initial velocity by **sinӨ**: v_yi = (40 m/s) sin (30) = 40 (0.5) = 20 m/s To find the time that the dart is in the air, we can use the equation **v_f = v_i + at**. We know that the initial vertical velocity is 20 m/s and at the peak of the flight, the vertical velocity will be 0 m/s. The acceleration due to gravity is -10 m/s². Plugging these values in yields: v_f = v_i + at (0 m/s)= (20 m/s) + (-10 m/s²) t -20 = -10t t = 2 seconds. Remember that this is the time for only the first half of the flight, the half it spends traveling upwards. Total time in the air will be double this value, or **4 seconds**. To calculate the velocity in the x-direction, we can multiply the initial velocity by **cosθ**: v_x = (40 m/s) cos (30) = 40 (0.87) ≈ 35 m/s Combining this information, we can calculate how far the dart will travel: **d= vt** d = (35 m/s)(4 s)) = **140 meters**.

Question 53

True or false: Normal force only exists in the presence of gravitational force.

Answer 53

This statement is **false**. Any object in contact with and exerting a force on surface will generate a reaction force equal to that force and perpendicular to the surface - this is called the normal force. The reason an object is exerting a force on a surface doesn't need to be gravity - for instance, a car crashing into a solid wall will experience a normal force from the wall.

Question 54

What are the units for force?

Answer 54

Force is measured in newtons. Force is calculated as mass multiplied by acceleration, so the units for a newton must be equal to kilograms (the units for mass) multiplied by m/s² (the units for acceleration). N = kg(m/s²)

Question 55

Newton’s second law says that acceleration is directly proportional to force, or specifically to the net force, and inversely proportional to the \_\_\_\_.

Answer 55

Newton’s second law says that acceleration is directly proportional to force, or specifically to the net force, and inversely proportional to the **mass**. This is represented by the equation Force=(mass)(acceleration), or alternatively, acceleration = force/mass.

Question 56

True or false: Two objects exerting an equal and opposite force on each other will experience the same magnitude of acceleration because force and acceleration are directly proportional.

Answer 56

This statement is **false**. Two objects exerting equal and opposite forces on each other will experience different accelerations if their masses are different. This concept is represented by Newton’s second law: Force=(mass)(acceleration). The accelerations will only be the same if the masses are equal. Because this question does not specify what the mass of each object is, we cannot assume that the acceleration will be equal.

Question 57

What is the gravitational force acting between a 4 x 10⁵ kg medical research space station and a 6 x 10²² kg asteroid if they are 5 x 10⁴ m apart?

Answer 57

For cases not involving an object on the surface of the Earth, we need to use the following equation. **Force_{gravitational} = (G)(m₁)(m₂)/r²** where G is the universal gravitational constant, m₁ is the mass of one object, m₂ is the mass of the other object, and r is the distance between the two objects. Remember to convert values given to SI units (kilograms and meters) prior to using this equation. Plugging in the provided values to the following equation yields: Force_{gravitational} = (G)(6 x 10²² kg)(4 x 10⁵ kg) / (5 x 10⁴ m)² = (G)(24 x 10²⁷ kg²) / (25 x 10⁸ m²) = ~(G)(1 x 10¹⁹ kg²/m²) Be careful with your estimation here! We rounded the numerator up to 25 x 10²⁷ kg² in order to get approximately (G)(1 x 10¹⁹) newtons. When you round the numerator up, it means that your estimated answer is going to be slightly larger than the true answer. This means that on the MCAT, you want to select an answer choice that is slightly less than (G)(1 x 10¹⁹) newtons if one is available. In this case, the true value will be (G)(0.96 x 10¹⁹) = (G)(9.6 x 10¹⁸) newtons.

Question 58

What is the coefficient of kinetic friction between the shoe covers used in the operating room and the tile floor, if an 80 kg surgeon goes sliding across the floor at a constant velocity when acted upon by a force of 2300 N?

Answer 58

We can calculate the coefficient of kinetic friction using the equation **F_kinetic = μN**. The surgeon is sliding at constant velocity, which means they are not accelerating, so there is no net force. No net force means that the forward force causing the surgeon to slide must be perfectly balanced by the force of kinetic friction, which opposes the surgeon’s motion. Because of this, we can set F_kinetic = 2300 N. F_kinetic = μN 2300 N = μ (80 kg)(10 m/s²) 2300 N = μ (800 N) 2300 N / 800 N = μ **~3 = μ**

Question 59

What force will need to be applied to start sliding a 60 kg patient from rest in one bed to the next if the coefficient of static friction is 0.75?

Answer 59

In order to determine how much force needs to be applied, we need to calculate the force that must be overcome. Since we are concerned about starting to move the patient from rest, we need to overcome the force of static friction. We can use the following equation: **F_static = μN**. F_static is the force due to static friction, μ is the coefficient of static friction, and N is the normal force. F_static = μN = (0.75)(60 kg)(10 m/s²) = (3/4)(600 N) = (1800 N/4) = **450 N** If the patient is going to be moved, this 450 N force of static friction must be overcome, so physicians and nurses moving the patient must apply **a force greater than 450 N.**

Question 60

What is the gravitational force a 35 kg person standing on the Earth's surface exerts on the Earth? (The gravitational constant G = 6.67 x 10^-11 m³/kg\*s²)

Answer 60

Gravity is an attractive force that exists between any two masses. Every piece of matter in the universe exerts some amount of gravitational attraction on every other mass. This means the Earth exerts an attractive force on us, and we also exert an equal and opposite attractive force on Earth. When discussing the gravitational attraction between the Earth and an object on its surface, we can calculate gravitational force as **Force=(mass)(acceleration due to gravity)** = (35 kg)(10 m/s²) = 350 N. The Earth exerts a 350 N force on this person and this person exerts a **350 N** force on the Earth.

Question 61

Will the acceleration of a mobile x-ray machine be constant if a constant, nonzero net force is applied to push it between inpatient rooms in the hospital? Why?

Answer 61

**Yes**. Newton's second law states that acceleration is directly proportional to the net force applied. If a constant net force is applied to the machine, its acceleration will be constant as well.

Question 62

What force needs to be applied in order to accelerate a 9 mg sample of blood at 40 m/s2?

Answer 62

Newton’s second law says that acceleration is directly proportional to the net force. This is expressed by F = ma, where “m” represents mass “a” represents acceleration. For our answer F to come out in newtons (kg\*m/s²), "m" must be in kilograms and "a" must be in m/s². F = (9 x 10^-3 g)(40 m / s²) = (9 x 10^-6 kg)(40 m / s²) = 360 x 10^-6 N = **3.6 x 10^-4 N**

Question 63

A car starts from rest and accelerates at 10 m/s2 for 4 seconds. How far does it travel?

Answer 63

To solve this problem, we must remember use the formula **d = v_i(t) + (1/2) at²**. Plugging in the values given yields: ``` d = v<sub>i</sub>(t) + (1/2) at<sup>2</sup> d = (0 m/s)(4 s) + (1/2)(10 m/s<sup>2</sup>) (4 s)<sup>2</sup> d = 0 + (1/2)(10)(16) d = **80 meters** ```

Question 64

A motorcyclist initially traveling at 70 m/s accelerates at a constant acceleration to a speed of 130 m/s in 10 seconds. How far did he travel?

Answer 64

To solve this problem, we can remember to use the formula **d = (½)(v_i + v_f)(t)**. Plugging in the values given yields: ``` d = (½) (70 m/s + 130 m/s)(10 s) d = (½)(200 m/s)(10 s) d = **1000 m** ``` To help remember this formula, just remember that when acceleration is constant (which will be the case on the MCAT), the average velocity over a period of time will simply be the average of the initial and final velocities, or (½)(v_i + v_f). Then distance traveled is just this average velocity multiplied by time.

Question 65

If a car accelerates from rest to a velocity of 30 m/s over 50 meters, what is the acceleration of the car, assuming it remains constant?

Answer 65

To solve this problem, we can remember to use the formula **v_f² = v_i² + 2ad**. Plugging in the given values yields: v_f² = v_i² + 2ad (30 m/s)² = (0 m/s)² + 2a(50 m) 900 = 100a 9 m/s² = a

Question 66

True or false: Speed is a measure of the change in distance over time.

Answer 66

This statement is **true**. Speed is the measure of change in distance over time.

Question 67

How fast would a ball be falling if it is dropped and allowed to accelerate for 4 seconds? Assume no air resistance.

Answer 67

We can use the formula **v****_f****= v****_i** **+ at** to solve this problem. Plugging in the given values yields: v_f = v_i + at v_f = 0 m/s + (10 m/s²)(4 s) v_f = **40 m/s**

Question 68

An object is falling at its terminal velocity. If we increase the object’s mass by a factor of nine without affecting its aerodynamics, what will happen to that terminal velocity? (Assume that the force of air resistance on an object is proportional to the object's velocity squared.)

Answer 68

**It will triple** At terminal velocity, the force of gravity must be equal to the force of air resistance. If the mass is increased by a factor of nine, then the gravitational force would increase by a factor of nine, since the force of gravity is equal to mg. In order for the force of air resistance to also increase by a factor of nine, the velocity would have to be tripled. This is because the force of air resistance is proportional to the square of velocity.

Question 69

If a juggler throws a ball straight up at a speed of 25 m/s, how long will it take to come back down?

Answer 69

If we look at the first half of the trip as the ball travels upwards, it starts at a velocity of 25 m/s, and at the peak of its trajectory, it will have a velocity of 0 m/s. We can use the formula **v_f = v_i + at** to calculate time. Plugging in these values and the acceleration due to gravity yields: v_f = v_i + at 0 m/s = 25 m/s + (-10 m/s²) t -25 = -10t 2.5 seconds = t However, 2.5 seconds is only the time needed to reach the top of the trajectory. We must multiply this number by 2 to account for the time it takes the ball to come back down, yielding **5 seconds**.

Question 70

If a bullet is fired at 10 m/s at an angle of 60 degrees above the horizontal, what will be its horizontal velocity right before it hits the ground? (Note that sin 60 = 0.87 and cos 60 = 0.5.)

Answer 70

Because there are no forces exerted on this object in the horizontal direction, the initial horizontal velocity will be the same as the final horizontal velocity. Therefore, we just need to break down the initial velocity given into its components. We can calculate the x-component as follows: ``` v<sub>ix</sub> = v<sub>i</sub> cosθ v<sub>ix</sub> = (10 m/s) cos (60) v<sub>ix</sub> = (10 m/s) (0.5) v<sub>ix</sub> = **5 m/s** ```

Question 71

If a baseball player throws a ball at 10 m/s at 60 degrees above the horizontal, what is the horizontal distance that the ball will travel before it lands? (sin 60 = 0.87 and cos 60 = 0.5)

Answer 71

In order to answer this question, we need to find: (1) the initial velocity of the ball in the y-direction, (2) the total time the ball spends in the air, and (3) the velocity of the ball in the x-direction. First, let’s calculate the ball’s initial vertical velocity: v_iy = (v_i)sinθ v_iy = (10 m/s) sin (60) v_iy = (10 m/s) (0.87) v_iy = 8.7 m/s Now, we can calculate the total time that the ball spends in the air. We know that the initial vertical velocity is 8.7 m/s, and at the peak of the flight, the vertical velocity will be 0 m/s. The acceleration will remain constant at -10 m/s². We can plug these values into the equation v_f = v_i + at: v_f = v_i + at (0 m/s) = (8.7 m/s) + (-10 m/s²) t -8.7 = -10t t = 0.87 seconds. Remember, this is the time required for only the first half of the flight, the half spent traveling upwards. The total time in the air will be double this value, or 1.74 seconds. Next we can calculate the ball’s velocity in the x-direction, which will remain constant: v_x = v_icosθ v_x = (10 m/s) cos (60) v_x = (10 m/s) (0.5) v_x ≈ 5 m/s Finally, we can combine this information to solve for the distance that the ball travels. We know that the horizontal velocity is about 5 m/s and that the ball is in the air for 1.74 seconds. We can thus calculate: ``` d= vt d = (5 m/s)(1.74 s) d = 8.7 meters ```

Question 72

True or False: A constant force applied to an object will cause it to travel at a constant velocity.

Answer 72

**This is false**. A constant net force will always cause a constant acceleration – and therefore a changing velocity. Additionally, a constant force will cause a constant (non-changing) acceleration, it will NOT cause an object to accelerate faster and faster.

Question 73

True or False: You can be accelerate a ball horizontally across the room by throwing it.

Answer 73

**False**. To accelerate, an object but be either 1) in contact with the object creating the force, or 2) be under the influence of a field force (e.g., gravitational or electrical) at that exact moment. Thus, the ball only accelerates horizontally during the brief time it is in contact with the object creating the horizontal force – in this case, your hand.

Question 74

When you see “Constant Velocity” or “Constant Speed" on the MCAT, what are the 5 conditions you should immediately know?

Answer 74

When you see “Constant Velocity” or “Constant Speed” THINK: 1. **No acceleration** 2. **No net force** 3. **All forces sum to zero** 4. **No change in direction** 5. **The object is in equilibrium**

Question 75

If there is no net force, can there be acceleration?

Answer 75

**No**, with no net force, there can be no acceleration. If force increases, acceleration increases. With no acceleration there must be no net force, although individual forces may still be occurring.

Question 76

If a projectile has a vertical velocity of 100 m/s, how many seconds will it take to reach maximum height and what will be its average velocity?

Answer 76

It will take 10 seconds to reach max height. Its average velocity will be 50 m/s

Question 77

If a projectile has an initial vertical velocity of 30 m/s, how long will it be in the air, how high will it go, and what will be its average velocity during the entire trip?

Answer 77

It will take 3 seconds to reach max height, and will be in the air for 6 seconds total. It will travel an average velocity of 15 m/s during the upward trip for 3 seconds, which means max height will be 45m. Its average velocity for the return trip will be equal in magnitude to its average velocity for the upward trip, but opposite in direction, so the average velocity during the entire trip will be 0 m/s. Alternately, you could reason that since the average velocity is displacement/time, and the displacement of the complete trip is zero, the average velocity is also zero.

Question 78

Define “range” in projectile motion

Answer 78

Range, or horizontal distance traveled, is a new value asked for in projectile motion. It is the product of velocity in the x-direction (V_x) and time (t). ## Footnote **Range = V_x(t)**

Question 79

When you see “projectile motion”, what are the 7 things you should always think.

Answer 79

When you see projectile motion, THINK: 1. **Horizontal velocity never changes** (ignoring air r) 2. **Horizontal acceleration always = 0** 3. **Vertical acceleration always = 10m/s² downward** 4. **Vertical behavior is exactly symmetrical** 5. **Time in air depends on V_y only** 6. **Range depends on both V_x and V_y** 7. **Time is always same for x and y components of the motion**

Question 80

Why does range, or horizontal displacement, depend on both vertical and horizontal velocity?

Answer 80

Because vertical velocity determines how long the object is in flight, range depends on both vertical and horizontal velocity. So, the longer an object is in flight, the more time it will have to travel horizontally. Horizontal velocity will determine how far it travels within the time limits put on it by the vertical velocity.

Question 81

Two students throw identical balls into the air with identical initial total velocities of 40 m/s. Student A throws his ball at a 50 degree angle with respect to the ground, and Student B throws his ball at a 40 degree angle. In comparison to Student A's ball, Student B's Ball will remain in the air for a: A) longer period of time, but travel a smaller horizontal distance B) shorter period of time, but travel the same horizontal distance. C) longer period of time, and travel a greater horizontal distance. D) shorter period of time, but travel a greater horizontal distance.

Answer 81

Student B's ball will have a greater horizontal component of velocity and a smaller vertical component. A smaller vertical velocity always means less time in the air, making answers B and D the only possible choices. The optimum launch angle for a maximum range is 45 degrees. Because the launch angle for both balls has deviated exactly the same amount from this optimum, they will travel the same distance. **Answer B is thus correct.**

Question 82

Name 3 factors that affect the magnitude of air resistance

Answer 82

1. Cross-sectional area: **greater cross-sectional area=more air resistance** 2. Shape: **less aerodynamic = more air resistance** 3. Velocity: **increased velocity = more air resistance**

Question 83

At terminal velocity, what two forces are in balance?

Answer 83

At terminal velocity, the object has stopped accelerating and the forces of **gravity** and **air resistance** are balanced.

Question 84

Remember that boiling point is defined as the temperature at which the vapor pressure of a solution is _________ the atmospheric pressure. A decrease in vapor pressure makes this point more difficult to achieve, resulting in a higher boiling temperature.

Answer 84

Remember that boiling point is defined as the temperature at which the vapor pressure of a solution is **equal to** the atmospheric pressure. A decrease in vapor pressure makes this point more difficult to achieve, resulting in a higher boiling temperature.

Question 85

What is the chemical formula for **sulfate**

Answer 85

SO₄^2-

Question 86

What is the chemical formula of **nitrate**? What is that of **nitrite**?

Answer 86

**Nitrate = NO₃^-** **Nitrite = NO₂^-**

Question 87

In β-minus decay, a ______ is converted to a ______ as an electron is emitted.

Answer 87

In β-minus decay, a **neutron** is converted to a **proton** as an electron is emitted.

Question 88

What is the function of adding boiling chips in the process of distillation?

Answer 88

When transitioning from liquid to gas during boiling, **the liquid needs nucleation sites, or places to start forming bubbles**. This is typically achieved either by scratching the inside of the flask or **by introducing boiling chips**.

Question 89

What does vacuum distillation accomplish?

Answer 89

Next, remember that boiling occurs when the P_vap of the substance in question equals the P_atm. Typically, we boil substances by increasing the temperature, thereby increasing P_vap. **Alternatively, however, we can lower boiling point by reducing P****_atm****, which can be accomplished through the introduction of a vacuum.** Vacuum distillation is often used when components have very high boiling points and would otherwise be difficult to distill.

Question 90

Answer 90

Question 91

Describe two different methods to find the answer of this question: A mass of 10 kg is dropped from a height of 20 m. Ignoring air resistance, what is the maximum speed achieved by the mass? (assume g = 10 m/s²)

Answer 91

Use gravitational potential energy, PE=mgh to find the maximum Kinetic energy, KE=PE. Using this, we know KE= ½(m)(v²) and solve for v. You also could have arrived at the correct answer using the kinematics equation v_f² = v_o² + 2a∆x, where ∆x = 20 m, v_o = 0 m/s, and a = 10 m/s².

Question 92

Answer 92

Question 93

Answer 93

Question 94

What is unique about H₂ with Pd?

Answer 94

It will reduce all alkenes and alkynes to **alkanes**.

Question 95

What do you know about the gibbs free energy of a reaction if the Keq is greater than 1?

Answer 95

This means that the gibbs free energy is a negative number, indicating a spontaneous reaction.

Question 96

Answer 96