Exam 2 Flashcards by Sera Cook

If a car is moving to the left with constant velocity then we can conclude that the net force is…

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An object cannot remain at rest unless

The net force is 0

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An object will have constant acceleration if the net force acting on it is…

Constant in magnitude and direction

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Two forces are applied to an object: a force of 10 N at 0 degrees and a force of 4 N at 180 degrees. What is the net force on the object?

6N at 0 degrees

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A 2 kg block is acted upon by two forces: 3 N (directed to the right) and 4N (directed to the left). What is the acceleration of the block in m/s2?

.5 to the left

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A 2 kg block is acted upon by two forces: 3 N (directed to the right) and 4N (directed to the left). What can you say about the block’s motion?

It could be moving to the left, moving to the right, or be instantaneously at rest.

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A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be __________.

Moving with constant non 0 acceleration

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A large truck collides head-on with a small car. The car is severely damaged as a result of the collision. According to Newton’s third law, how do the forces acting between the truck and car compare during the collision?

The force on the truck is equal to the force on the car

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A small car collides with a large truck. Is the acceleration experienced by the car greater than, less than, or equal to the acceleration experienced by the
truck?

Greater than

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An object is at rest on a tabletop. Earth pulls downward on this object with a force equal in magnitude to mg. If this force serves as the action force, what is the reaction force in the action–reaction pair?

The object pulling upward on earth

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The same net force is applied to two different objects. The second object has twice the mass of the first object. Compare the acceleration of the two
objects.

The acceleration of object 1 is twice the acceleration of object 2

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An object is moving with constant velocity. Which of the following best describes the force(s) acting on the object?

The net force acting on the object is 0

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Squids propel themselves by expelling water from a contractile mantle (jet propulsion). If a squid wished to accelerate up and to the right, in which direction should it eject water?

Down and to the left

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A car accelerates northward from a stoplight. What is the direction of the net force acting on the car?

Northward

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A car is traveling southward and slowing down. What is the direction of the net force acting on the car?

Northward

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A car is traveling westward with constant speed. What is the direction of the net force acting on the car?

Zero

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A skydiver is parachuting downward with constant speed. What is the direction of the net force acting on the skydiver?

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A baseball, during its flight from pitcher to catcher, experiences no air resistance. What is the direction of the net force acting on the baseball?

Downward

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A book weighing 5 N rests on top of a table. A downward force of magnitude 5 N is exerted on the book by the force of

Gravity

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The reaction to the force in the previous question is a force of magnitude _____, exerted on the _____ by the _____. Its direction is _____ .

5 N / earth / book / upward

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A book weighing 5 N rests on top of a table. An upward force of magnitude _____ is exerted on the _____ by the table.

5 N/ Book

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The reaction to the force in the previous question is a force of magnitude _____, exerted on the _____ by the _____. Its direction is _____.

5 N / table / book / downward

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An object is hanging by a string from the ceiling of an elevator. The elevator is slowing down while moving upward. What is the magnitude of the tension in the string?

The magnitude of the tension in the string is less than the magnitude of the weight of the object

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An object is hanging by a string from the ceiling of an elevator. The elevator is moving upward with a constant speed. What is the magnitude of the tension in the string?

The magnitude of the tension in the string is equal to the magnitude of the weight of the object.

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In general, how does the coefficient of static friction compare to the coefficient of kinetic friction for the same two materials?

The coefficient of static friction is greater than the coefficient of kinetic friction.

A packing crate is sitting at rest on an inclined loading ramp. How does the magnitude of the force of static friction compare to the other forces acting on the crate?

The magnitude of the force of static friction is equal to the magnitude of the component of the weight of the crate parallel to the inclined ramp.

A large crate filled with physics laboratory equipment must be moved up an incline onto a truck. The crate is at rest on the incline. What can you say about the force of friction acting on the crate?

The frictional force points up the incline

A physicist attempts to push the crate up the incline. The physicist senses that if he applies slightly more force the crate will move up the incline but cannot muster enough strength to get the motion started. What can you say now about the force of friction acting on the crate?

It points down the incline

A baggage handler at an airport applies a constant horizontal force with magnitude F to push a box, of mass m, across a rough horizontal surface with a very small constant acceleration a. What is the correct expression of Newton's 2nd law for this scenario, given a frictional force of f ?

F-f=ma

A baggage handler at an airport applies a constant horizontal force with magnitude 18 N to push a 2.0 kg box, across a rough horizontal surface with a coefficient of kinetic friction of 0.509. What is the acceleration of the box.

F=uN (.509)(2)(9.81)=9.99 F=ma (18-9.99)/2=4 4.0

A 6-kg bucket of water is being pulled straight up by a string at a constant speed. What is the tension in the rope?

about 60N

A 6-kg bucket of water is being pulled straight up by a string at a constant speed. At a certain point the speed of the 6-kg bucket begins to change. The bucket now has an upward constant acceleration of magnitude 3 m/s2. What is the tension in the rope now?

About 78

A block of mass m1 slides on a frictionless tabletop. It is connected to a string that passes over a pulley and suspends a mass m2. Suppose m1 and m2 are both increased by a factor of 2. Does the acceleration of the blocks increase, decrease, or stay the same?

Stay the same

A block of mass m1 slides on a frictionless tabletop. It is connected to a string that passes over a pulley and suspends a mass m2. Suppose m1 and m2 are both increased by a factor of 2. Does the tension in the string increase, decrease, or stay the same?

Increase

A child goes down a playground slide with an acceleration of 1.26 m/s2. Find the coefficient of kinetic friction between the child and the slide if the slide is inclined at an angle of 31.0 degrees below the horizontal.

ma=mgsin(*)-umgcos(*) | .451

When a 9.00 kg mass is placed on top of a vertical spring, the spring compresses 4.26 cm. Find the force constant, k, of the spring in SI units.

2.07 K=f/d

An object weighing 20 N moves horizontally toward the right a distance of 5.0 m. What is the work done on the object by the force of gravity?

The work done on the object by the force of gravity is zero joules..

A ball is thrown straight upward. How does the sign of the work done by gravity while the ball is traveling upward compare with the sign of the work done by gravity while the ball is traveling downward?

Work done by gravity is negative while the ball is traveling upward and positive while the ball is traveling downward.

A person applies a 50 N force on a crate, causing it to move horizontally at a constant speed through a distance of 10 m. What is the net work done on the crate?

If the net work done on an object is positive, what can you conclude about the object's motion? Assume the object is in the absence of any other forces or friction.

The object is speeding up

If the net work done on an object is zero, what can you determine about the object's kinetic energy?

It remains the same

What is the minimum work done by the heart to pump 340 g of blood from a person's foot to his heart 1.5 m away? Use g = 10 m/s2.

5.1J

A 35 kg boy climbs a 15 m rope in 35 s. What was his average power output? Use g = 10 m/s2.

150 W

During each heartbeat, about 80 g of blood is pumped into the aorta in approximately 0.2 s. During this time, the blood is accelerated from rest to about 1 m/s. What is the average force on the blood during this time?

.4 N

During each heartbeat, about 80 g of blood is pumped into the aorta in approximately 0.2 s. During this time, the blood is accelerated from rest to about 1 m/s. What is the acceleration of the blood during this time, in m/s2?

During each heartbeat, about 80 g of blood is pumped into the aorta in approximately 0.2 s. During this time, the blood is accelerated from rest to about 1 m/s. What distance does the blood cover in this time, assuming the acceleration is constant?

10 cm

During each heartbeat, about 80 g of blood is pumped into the aorta in approximately 0.2 s. During this time, the blood is accelerated from rest to about 1 m/s. How much work is done by the heart on the blood during this time?

.04 J

During each heartbeat, about 80 g of blood is pumped into the aorta in approximately 0.2 s. During this time, the blood is accelerated from rest to about 1 m/s. If the heart beats 60 times in 1 minute, how much blood moves through the heart in 10 hours?

2880 kg

During each heartbeat, about 80 g of blood is pumped into the aorta in approximately 0.2 s. During this time, the blood is accelerated from rest to about 1 m/s. What is the power output of the heart needed to perform one heartbeat?

.2 W

Is it possible to do work on an object that remains at rest?

A baseball pitcher throws a ball at 90 mph and the catcher stops it in her glove. Is the work done on the ball by the pitcher positive, negative, or zero?

Positive

A baseball pitcher throws a ball at 90 mph and the catcher stops it in her glove. Is the work done on the ball by the catcher positive, negative, or zero?

Negative

A farmhand pushes a 23 kg bale of hay 3.6 m across the floor of a barn. If she exerts a horizontal force of 91 N on the hay, how much work has she done, in Joules?

W=Fd 330

The coefficient of kinetic friction between a suitcase and the floor is 0.272. If the suitcase has a mass of 80.0 kg , how far in meters can it be pushed across the level floor with 660 J of work?

3.09 W=Fd F=Ma 660/(80*.272*9.81)

A 9.50 g bullet has a speed of 1.30 km/. What is its kinetic energy in joules?

8030 KE=(1/2)mV^2 change the mass to kg and the speed to m/s.

How much work in Joules is needed for a 78 kg runner to accelerate from rest to 7.5 m/s?

2200 W=mv^2(1/2)

A 70 kg bicyclist rides his 9.8 kg bicycle with a speed of 15 m/s. How much work in Joules must be done by the brakes to bring the bike and rider to a stop?

-9000 | W=(1/2)(m)(v(final)-v(initial))

A 70 kg bicyclist rides his 9.8 kg bicycle with a speed of 15 m/s. How far in meters does the bicycle travel if it takes 4.5 s to come to rest?

A spring with a force constant of 4.0×104 N/m is initially at its equilibrium length. How much work in Joules must you do to stretch the spring 0.060 m ?

W=(1/2)kx^2 72

A spring with a force constant of 4.0×104 N/m is initially at its equilibrium length. How much work in Joules must you do to compress the spring 0.060 m?

W=(1/2)kx^2 72

Two identical balls are thrown vertically upward. The second ball is thrown with an initial speed that is twice that of the first ball. How does the maximum height of the two balls compare?

The maximum height of the second ball is four times that of the first ball.

Two objects are moving at equal speed along a level, frictionless surface. The second object has twice the mass of the first object. They both slide up the same frictionless incline plane. Which object rises to a greater height?

The two objects rise to the same height.

When a ball is thrown upward, its mechanical energy, E = K + U, is constant with time if air resistance can be ignored. How does vary with time if air resistance cannot be ignored?

Mechanical energy decreases

An object is thrown upward to a person on a roof (ignore air resistance). At what point is the object's kinetic energy at maximum?

When the object is released

An object is thrown upward to a person on a roof (ignore air resistance). At what point is the object's kinetic energy equal to the potential energy?

when the object rises to half its greatest height

An object is thrown upward to a person on a roof (ignore air resistance). At what point is the object's potential energy at maximum?

When the object reaches it’s greatest height

Ball 1 is thrown to the ground with an initial downward speed; ball 2 is dropped to the ground from rest. Assuming the balls have the same mass and are released from the same height, is the change in gravitational potential energy of ball 1 greater than, less than, or equal to the change in gravitational potential energy of ball 2?

Equal

The work-energy theorem states that a force acting on a particle as it moves over a ______ changes the ______ energy of the particle if the force has a component parallel to the motion.

Distance/ kinetic

To illustrate the work-energy concept, consider the case of a stone falling from xi to xf under the influence of gravity. Using the work-energy concept, we say that work is done by the gravitational _____, resulting in an increase of the ______ energy of the stone.

Force/ kinetic

A spring is stretched from x = 0 to x = d, where x = 0 is the equilibrium position of the spring. It is then compressed from to x = 0 to x = -d. What can be said about the energy required to stretch or compress the spring?

The same amount of energy is required to either stretch or compress the spring.

Two identical springs are attached to a wall on one end a mass on the other end. MA is greater than MB and both masses can slide on a frictionless surface. Both springs are compressed the same distance, d. Which of the following statements describes the energy required to compress spring A and spring B?

Spring A requires more energy than spring B

You throw a ball upward and let it fall to the ground. Your friend drops an identical ball straight down to the ground from the same height. Is the change in kinetic energy of your ball greater than, less than, or equal to the change in kinetic energy of your friend's ball?

Equal

Find the gravitational potential energy in Joules of an 83 kg person standing atop a cliff at an altitude of 120 m above the ocean. Use sea level as the location for y = 0.

98000 | PE=mgh

A 0.38 kg pendulum bob is attached to a string 1.2 m long. What is the change in the gravitational potential energy (in Joules) of the bob as the it swings from point A to point B in the figure? 35 degrees

-.81

At an amusement park, a swimmer uses a water slide to enter the main pool. If the swimmer starts at rest, slides without friction, and descends through a vertical height of 2.61 m, what is her speed in m/s at the bottom of the slide?

7.15 PE=KE Mgh=(1/2)mV^2

A 0.26-kg rock is thrown vertically upward from the top of a cliff that is 32 m high. When it hits the ground at the base of the cliff, the rock has a speed of 32 m/s. Assuming that air resistance can be ignored, find the initial speed in m/s of the rock.