Chem/Physics Flashcards
Displacement
Change in position of an object. We use the symbol (delta)Δx for displacement, where Δdelta means “change.” A vector quantity with units of distance.
Distance
Total amount the object has moved.
This depends on the whole path traveled, not just the starting and ending points. Distance traveled is always a non-negative number. *****
A scalar quantity with units of distance
Mistakes ppl make with distance vs displacement
People sometimes think that distance and displacement are just different names for the same quantity.
However, distance and displacement are different concepts. If an object changes direction in its journey, the total distance traveled will be greater than the displacement between those two points.
Mercury has specific gravity of 13.6 The column of mercury in the barometer below has a height h=76 cm. If a similar barometer were made with water, what would be the approximate height h of the column of water?
Answer= 1034 cm. Atompshereic pressure supports the column of fluid, the pressure at the bottom of the column must be equal to the atm pressure because atmosphere pressure is forcing the liquid into the column. If the pressure at the bottom of the column were not atmospheric, there would be a pressure differential adn more liquid would flow into the column. The pressure is equal to pgh. If p is dec by a factor of 13.6, the height must be inc by the same factor.
A helium balloonwill rise into the atmosphere until: A. the temperature of the heloim inside the balloon is equal to the temperature of the air outside the balloon; B. the mass of the helium inside the balloon is equal to the mass of the air outside of the balloon; C. the volume of the helium is equal to the volume of the air it displaces; D. the density of the helium in the balloon is equal to the density of the air surrounding the balloon
-D
A child’s bathub toy has a density of 0.45 g/cm^3. What fraction of the toy floats above the water?
The specific gravity must be how much is under the water. 45% must be under water, so 55% must be above hte water. To solve this problem, set the buoyant force equal to the weight of the toy. *** to find the fraction of the toy above water, sutbract the submerged fraction from 1**
Three containers are filled with water to a depth of 1 meter. At the bottom of which container is the pressure the greatest?
Pressure depends only on depth and density, not on the shape of the container so the pressure is the same at the bottom of all the containers (despite having different shapes).
A weather balloon travels upwards for 6 km while the wind blows it 10 km north adn 8 km east. Approximately what is its final displacement from its initial position?
Review explanation answer’s calculations. If the balloon travels in three perpendicular directions, this can be considered three displacement vectors. Answer is 14 km.
The Earth moves around the sun at approximately 30 m/s. Is the Earth accelerating?
Answer= acceleration is the rate of change of velocity. Since velocity is a vector, it specifies magnitude and direction. Even if speed stays constant, the direction of the Earth’s motion is constantly changing. Therefore the earth is accerating, so the anwer is yes because the velocity is not constant.
A car accereates at a constant rate from 0 to 25 m/s over a distance of 25 m. Approximately how long does it take the car to reach the velocity of 25 m/s?
Answer= 2s; Question implies variable of initial velocity which is zero. The average velocity of any constantly accelerating object that starts with zero velocity is the final velocity divided by 2. So the velocity is 12.5 m/s, making time 2 s. Look in book to review explanation answer’s calculations.
A driver moving at a constant speed of 20 m/s sees an accident up ahead and hits the brakes. If the car decelerates at a constant rate of -5 m/s^2, how far does the car go before it comes to a stop?
Answer= 40 m, look in book for answer calculations and explanation.
Suppose that you constructed a simple barometer using water instead of mercury. Approximately how high woul the water raise in the tube at sea level? Note specific gravity of mercury= 13.6.
Answer=10 m, height of hte substance in teh tub can be calculated using P atm= pgh. 101,325 Pa= (1000 kg/m^3) (10 m/s^2)h, so height = 10 m approximately. Can also use 1 atm= 760 mmHg, since mercury is 13.6 times denser than water, water will rise 13.6 times as high, or approximately 14 times higher.
Look in book for equation. Ammonia burns in air to form nitrogen dioxide and water. If 8 moles of NH3 are reacted with 14 moles of O2 in a rigid container with an intial pressure of 11 atm, what is the partial pressure of NO2 in the container when the reaction runs to completion? Assume constant temperature.
Answer= 4 atm; If the container began at 11 atm then each gas is contributing a pressure in accordance with its stoichioemtric coefficient. When the reaction runs to completion the only gas in the container is nitrogen dioxide, so the partial pressure of nitrogen dioxide is the total pressure. The volume and temperature of the container remains constant, so teh pressure is in accordance with teh stoichiometric coefficient of nitrogen dioxide.
A person jumps into a pool foot-first. Where in the body is the hydrostatic pressure the greatest?
Answer= pressure=rowpXgXy, since density of water is constant throughout the pool, as is the gravity constant, only the pressure varies directly with depth. For this reason, the deepest or lowest body part listed among the answer choices is hte best answer so it should be your foot* every other answer was above the foot
A clump of malaria parasites blocks 1/4 of the cross sectional area of a horizontal, cylindrical artery. Which of the following statements is true regarding flow through the blocked area, assuming ideal flow?
Answer= Blood in the blocked area has a lower pressure……………B/c: the key impact of the blockage is that veloicty is increased based on the continuity equation, Q= AV= constant, A1v1=A2v2. if area is dec than velocity is INCREASED* since the equation stem assumes real flow, choice A presents the opposite effect and can be eliminated. Blood in the blocked area has the same potential energy as other areas of the vessel since the artery is horizontal. Blood in the blocked area will have a lower pressure, chpice C, according to Bernoulli’s equation: P+1/2pv+ pgy = constant, PE density is constant and velocity is increased in the blockage. If velocity is increased, then pressure must be decreased in the bloackage to compensate and maintain Bernoulli’s equation
While a regular sample of blood forms an upward meniscus in the tube, an infected sample forms a downward meniscus. Which of the following is most likely correct?
Answer= this question tests the concept of surface tension* an upward meniscus means that cohesive forces are greater than adhesive forces. This is because cohesive forces are between blood molecules and adhesive forces are between blood and the tube. If the meniscus is upwards, this means that blood preferentially interacts with itself. A downward men iscus is the opposite. Adhesive forces are higher than coehsive forces so the most likely change is tha cohesive forces decrease adn adhesive forces increase relative toregular blood, which is choice D. “Parasite presence decreases cohesive forces adn increases adhesive forces***”
The presence of parasites in the bloodstream increases the viscosity of blood. Which of the following statements is most likely to be true?
Answer= Based on the passage, severe infection involves a large number of parasites in the bloodstream. The question states that these parasites inc viscosity. Lack of viscosity is one of the assumptions of ideal flow, Answer “Blood flow is less ideal during severe infections.”
Two ions in the blood -q1 and +q2 carrying equal and opposite charges approach a uniform magnetic field at the same speed. Which of the following conditions is sufficient to guarantee a force on -q1 within the field that has a greater magnitude than that on +q2?
Answer: theta 1 is less than theta 2! the mvoement of charge in an electric field will result in a forc according to the equation F=qvBsintheta, notice that it does nto matter that ions carry oppsoite charges becasue thsi question is only asking about the magnitude of force in teh q term. Opposite charges will reverse the direction of force on movign charges. In option I, if -q1 moved faster than +q2, that would not guarantee agreater force on teh charge. it could move in the direction of the magnetic field and the sine term in teh force equation would bring the matngidue of force to zero. Option I is insufficnet, options II or III represent oppposite conditions and given that chocies A and B remain, only one of them must be true. Notice that, in the force equaton, theta refers to the angle between teh charge’s velocity and the gfiel.d In the diagram, theta decribes the angle between the charges’ velocities and the normal. the smaller theta is in teh diagram the greater the theta in teh force equation for charge -q1. notice thta as the theta in teh force eqution increases from 0 to 90 degrees, the sine term must also inc. that makes optoon II true, eliminating chocie B, and leaving choice A as the best answer.
All of the following expressions are equal to an Ohm except (power= IV=I^2R=V^2/R)
Answer: A/V–> Choice A comes from V=iR,with I replaced by C/sec, B comes from P= i^2 R, D comes from P=V^2/R
Voltage sources for alternating current are characterized by their average voltage, Vrms (Vrms= Vmax/ squarerrot 2) if the AC current delivered to a home by the electric company is delivered at 120 Vrms, what is the maximum voltage across an outlet?
A:170V, max voltage is given by vmax= squareroot [2] V rms, squr 2 X 120 V, = 1.4 X 120 V= 168 V which rounds to 170 V
Neurons send messages via electrical impulses along their axons. The impulse called an action potential is propagated when ions enter or exit the cell. Approximately 5.5 X 10^11 Na+ ions [er emeter cross the cell membrane during a second of the propagation of an action potetnal. What is the current caused by the flow of NA+ across 1 cm of the axon? (elementary charge = 1.6 X 10^-19 C)
A; 8.8 X 10^-10 C/s; the flow of ions per meter of axon per second is 5.5 X 10^11. the flow of Na+ ions in one centimeter of axon is: (5.5 X 10^11 Na+ ions/meter) X (1 meter/10^2 cm) = 5.5 X 10^9 Na+ ions/cm/sec ………….. each Na+ ion has charge equal to the elementary charge, teh charge of one proton. the total charge flowing across in one second is: 5.5 X 10^9 Na+ ions/meter) X( 1.6 X 10^-19 C/Na+ ion) = 8.8 X 10^-10 C/s
The resting voltage across the membrane of a neuron is measured at -70 mV. In multiple scelorisis, the axons of neurons lsoe their myelin sheath. This results in 30% decreased in teh resistance of the membrane. What is the current flow across one cm of an axon in a patient with multiple scherosis? Assume that the resistance of a healthy axon is 250 Momega cm.
A: Ohm’s law i= V/r. the resistnce of one cm of memebrane in a neuron with multipel sclerosis is 0.7 X 250 Momega, = 175 M omega, Do not forget to convert to SI units= i= V/R=7X 10^-2 V/ 1.75 X 10^8 omega= 4 X 10^-10, Answer = 4X10^-4 uA
An MRI has a megnetic field of 1.5 t. What force does the MRI haev on a hydrogen ion at rest in the human brain?
A: 0N, the force on the charge moving in a magnetic field due to a magnetic field is F= qvBsintheta. Sicne the hydrogen ion is at rest its velocity is 0 m/s and it will not experience a force due to the magnetic field of the MRI.
Consider a uniform magnetic field coming out of the page. There is a wire loop in teh plane of hte page. Which of the following would induce an electromotive force in the wire loop? I. Inc the magnitude of the magnetic field; II. Rotatig the wire loop to the right; III. Moving the wire loop vertically out of the page
A: C= I and II, meaning inc the mag. of the magnetic field, and II rotating the wire loop to teh right. Faraday’s law states that a changing magnetic field will induce an electromotive force EMG, in a wire. the goal of this problem is to figure otu which of hte options given produce a changing magnetic field with respect to teh wire. Changing the magnitude of the magnetic field, option I, certainly does this. eliminate answer choice D, since it does not include option I. moving the wire loop out of hte page moves it along the same magnetic field lines. This does not change anythign about the magnetic field felt by hte wire and will nto induce an electromotive force. Rotating the wire will change the magnetic field lines around the wire and induce an EMF.
Electrophoresis is used to separate proteins accordin to their mass. Proteins are placed into a gel matrix, and an electric field is applied. Which of the followign will increase the speed at which teh proteins move through the gel?
A: All of these things will change the magnitude of the force on teh proteins and therefore by Newton’s second law, chang ehow fast they accelerate from rest. The electric field kq/r^2 and the charge are directy related to the electric force felt by the protein. Increasing size of the pores will reduce the “drag” caused by the gel and allow the proteins to move faster. so- if you inc the size f the pores of the gel, inc the strength of the electric field, and inc hte charge on the protein all of these things will inc the speed at which the proteins move through the gel!
Ammonia reacts with water to form the ammonium ion and hydroxide ion as shown. According to the Bronstead-Lowry definition of acid and bases, what is the conjugate acid of ammonia?
A: NH4+, ammonia is the base so the conjugate acid of ammonia is NH4+; conjugate acid is a molecule AFTER it accepts a proton
Which of the following is the strongest base in aqeous solution? options Cl-, NH4+, F-, Br-
A:F-, NH4+ is an acid and the strongest base is the conjguate of the weakest acid, this is b/c KaKb=Kw, the respective stregnths of the membres of any conjugate pair are inversely related. What this question is really asking is to find the option with the weakest conjugate acid*** that is F- . As the bond strength of the haloen and the hydrogen increases, highest in HF, the strength of the acid decreases.
The addition of an electron withdrawing group to teh alpha carbon of a carboxylic acid will: structure of molecule aC-c=0 (c- also attached to OH look on page 235)…. a. inc the acidity of hte prton by making the OH bond more polar, B. inc hte acidity of the proton by making the OH bond stronger, C. decrease the acidity of the proton by making the OH bond more polar, D. dec the acidity of the proton by stabilzing the conjugate base
A:The electron withdrawing group will further polarize the Oh bond and polarization inc acidity in aq solution. Even if hte Oh bond became stronger, which it does not, this change would result in a weaker acid. Choice D is false, as stabliztion of the conjugate base would cause teh acid to be stronger more readily turning into the conjugate base. A is hte best answer, inc hte acidity of hte proton by making the OH bond more polar*
Suppose that a student prepares two acidic solutions. Solution A has a hydrogen ion concentration of 6.0 x 10^-5 M. Solution B has a hydrogen ion concentration of 1 X 10^-7 M. The pH of solution A differs from that of solution B by:
A: 2.8, pH of solution B is 7. pH of solution A is btw 4 and 5. This is b/c the H ion concnetration of 1 X 106-5 mol/L would result in a pH of 5, and a concentration of 1.0 X 10^-6 mol/L would result in a pH of 6. Additionally, if the hydrogen ion concentration is greater than a known value then teh value for the pH will be smaller adn vice versa. The only pH difference btw 7 and 4 to 5 is choice B 2.8.
An aqueous solution of 0.1 M HBr has a pH of:
pH=1, HBr is a strong acid, so it dissociates completely. The concentration of H+ ions will be equal to the cocnentration of HBr, the -log(0.1)= 1
An aqueous solution of 0.1 M HBr has a pH of:
pH=1, HBr is a strong acid, so it dissociates completely. The concentration of H+ ions will be equal to the cocnentration of HBr, the -log(0.1)= 1
Carbonic acid has a Ka of 4.3 X 10^-7. What is the pH when 1 mole of NaHCO3 is dissolved in 1 liter of water?
10.2 b/c Kw/Ka= Kb= 0.25 X10^-7. we set up the equilbirum expression, remember x in denominator is insignificant to cancel out, x= 1.5 X 10^-4 so the pOH isbtw 3 and 4, when subtract from 14 the pH will be between 10 and 11
Which of the following salts is the most basic? A. NaClO3; B. NH4Cl; C. KBr; D. NaCN
NaCN, because CN- is the conjugate base of a weak acid. the wak acid stronger conjugate base and CN- is a very strong base, choices A-C are conjugates of strong acid and therefore weaker bases. this is due to teh inverse relationship between the strength of conjugates.
A solution of soapy water has a pH of 10. What is the hydroxide ion concentration?
10^-4 M, if the pH is 10, the pOH is 4, it must be 4. If the pOH is 4, then the hydroxide ion cocnentration must be 10^-4 M. Chocie A gives the correct hydronium ion cocnegration, but thsi is nto what the question asks for.
A meteror with a mass of 1 kg moving at 20 km/s collides with Jupiter’s atmosphere. The meteor penetrates 100 km into the atmosphere and disintegrates. What is the average force on the meteor once it enters Jupiter’s atmosphere?
Answer= 2 X 10^3 N. At disintegration the velocity of the meteor is 0 m/s. the friction force acts on teh meteor such that its velocity decreases from 20 km/s to 0 m/s. That is the force does work equal to change in KE of the meteor* W=fd=F(100 km) = 1/2mvf^2-1/2mvi^2= 0.5 (1 g) (20 km/s)^2-0.5 (1 kg) (0 km/s)^2. So, F(100 X 10^3 m)= 0.5 (1 kg) ( 20 X 10^3 m/s)^2
