Question 1

A 1.0 kg-ball moving at 2.0 m/s perpendicular to a wall rebounds from the wall at 1.5 m/s.The change in the momentum of the ball is:

Accepted Answer

A) zero 
B) 0.5 N∙s away from wall 
C) 0.5 N∙s toward wall 
D) 3.5 N∙s away from wall 
E) 3.5 N∙s toward wall 
A) zero 
B) 0.5 N∙s away from wall 
C) 0.5 N∙s toward wall 
D) 3.5 N∙s away from wall 
E) 3.5 N∙s toward wall D

Question 2

Two spacemen are floating together with zero speed in a gravity-free region of space.The mass of spaceman A is 120 kg and that of spaceman B is 90 kg.Spaceman A pushes B away from him with B attaining a final speed of 0.5 m/s.The final recoil speed of A is:

Accepted Answer

A) 0 m/s 
B) 0.38 m/s 
C) 0.43 m/s 
D) 0.50 m/s 
E) 1.0 m/s 
A) 0 m/s 
B) 0.38 m/s 
C) 0.43 m/s 
D) 0.50 m/s 
E) 1.0 m/s B

Question 3

Blocks A and B are moving toward each other.A has a mass of 2.0 kg and a velocity of 50 m/s, while B has a mass of 4.0 kg and a velocity of -25 m/s.They suffer a completely inelastic collision.The kinetic energy lost during the collision is:

Accepted Answer

A) 0 J 
B) 1250 J 
C) 3750 J 
D) 5000 J 
E) 5600 J 
A) 0 J 
B) 1250 J 
C) 3750 J 
D) 5000 J 
E) 5600 J C

Question 4

Which one of the following statements is true?

Accepted Answer

A) the center of mass of an object must lie within the object 
B) all the mass of an object is actually concentrated at its center of mass 
C) the center of mass of an object cannot move if there is zero net force on the object 
D) the center of mass of a cylinder must lie on its axis 
E) none of the above 
A) the center of mass of an object must lie within the object 
B) all the mass of an object is actually concentrated at its center of mass 
C) the center of mass of an object cannot move if there is zero net force on the object 
D) the center of mass of a cylinder must lie on its axis 
E) none of the above

Question 5

The center of mass of Earth's atmosphere is:

Accepted Answer

A) a little less than halfway between the Earth's surface and the outer boundary of the atmosphere 
B) near the surface of the Earth 
C) near the outer boundary of the atmosphere 
D) near the center of the Earth 
E) none of the above 
A) a little less than halfway between the Earth's surface and the outer boundary of the atmosphere 
B) near the surface of the Earth 
C) near the outer boundary of the atmosphere 
D) near the center of the Earth 
E) none of the above

Question 6

Force:

Accepted Answer

A) equals the negative integral (with respect to distance)of the potential energy function 
B) is the ability to do work 
C) is the rate of change of doing work 
D) equals the time rate of change of momentum 
E) has dimensions of momentum multiplied by time 
A) equals the negative integral (with respect to distance)of the potential energy function 
B) is the ability to do work 
C) is the rate of change of doing work 
D) equals the time rate of change of momentum 
E) has dimensions of momentum multiplied by time

Question 7

The momentum of a system of particles is changing at the rate of 0.71 t + 1.2 t2, in kg∙m/s.The net force at t = 2.0 s

Accepted Answer

A) cannot be determined without knowing the masses of the particles. 
B) is 5.5 N 
C) is 3.1 N 
D) is 1.9 N 
E) cannot be determined without knowing the momentum at t = 0 
A) cannot be determined without knowing the masses of the particles. 
B) is 5.5 N 
C) is 3.1 N 
D) is 1.9 N 
E) cannot be determined without knowing the momentum at t = 0

Question 8

Cart A, with a mass of 0.2 kg, travels on a horizontal air track at 3 m/s and hits cart B, which has a mass of 0.4 kg and is initially at rest.After the collision the center of mass of the two cart system has a speed in m/s of:

Accepted Answer

A) 0 m/s 
B) 1.0 m/s 
C) 2.3 m/s 
D) 2.5 m/s 
E) 5.0 m/s 
A) 0 m/s 
B) 1.0 m/s 
C) 2.3 m/s 
D) 2.5 m/s 
E) 5.0 m/s

Question 9

A 64-kg woman stands on frictionless level ice with a 0.10-kg stone at her feet.She kicks the stone with her foot so that she acquires a velocity of 0.0017 m/s in the forward direction.The velocity acquired by the stone is:

Accepted Answer

A) 1.1 m/s forward 
B) 1.1 m/s backward 
C) 0.0017 m/s forward 
D) 0.0017 m/s backward 
E) none of these 
A) 1.1 m/s forward 
B) 1.1 m/s backward 
C) 0.0017 m/s forward 
D) 0.0017 m/s backward 
E) none of these

Question 10

The momentum of an object at a given instant is independent of its:

Accepted Answer

A) inertia 
B) mass 
C) speed 
D) velocity 
E) acceleration 
A) inertia 
B) mass 
C) speed 
D) velocity 
E) acceleration

Question 11

A particle moves along the x axis.Its momentum is graphed below as a function of time.Rank the numbered regions according to the magnitude of the force acting on the particle, least to greatest.

Accepted Answer

A) 1, 2, 3, 4 
B) 2, 3, 4, 1 
C) 1, 4, 3, 2 
D) 4, 3, 2, 1 
E) 2, 4, 3, 1 
A) 1, 2, 3, 4 
B) 2, 3, 4, 1 
C) 1, 4, 3, 2 
D) 4, 3, 2, 1 
E) 2, 4, 3, 1

Question 12

Sphere X, of mass 2 kg, is moving to the right at 10 m/s.Sphere Y, of mass 4 kg, is moving to the left at 10 m/s.The two spheres collide head-on.The magnitude of the impulse of X on Y is:

Accepted Answer

A) twice the magnitude of the impulse of Y on X 
B) half the magnitude of the impulse of Y on X 
C) one-fourth the magnitude of the impulse of Y on X 
D) four times the magnitude of the impulse of Y on X 
E) the same as the magnitude of the impulse of Y on X 
A) twice the magnitude of the impulse of Y on X 
B) half the magnitude of the impulse of Y on X 
C) one-fourth the magnitude of the impulse of Y on X 
D) four times the magnitude of the impulse of Y on X 
E) the same as the magnitude of the impulse of Y on X

Question 13

A thick uniform wire is bent into the shape of the letter "U" as shown.Which point indicates the location of the center of mass of this wire?

Accepted Answer

A) A 
B) B 
C) C 
D) D 
E) E 
A) A 
B) B 
C) C 
D) D 
E) E

Question 14

For a completely inelastic two-body collision the kinetic energy retained by the objects is the same as:

Accepted Answer

A) the total kinetic energy before the collision 
B) the difference in the kinetic energies of the objects before the collision 
C) 1/2Mv2com, where M is the total mass and vcom is the velocity of the center of mass 
D) the kinetic energy of the more massive body before the collision 
E) the kinetic energy of the less massive body before the collision 
A) the total kinetic energy before the collision 
B) the difference in the kinetic energies of the objects before the collision 
C) 1/2Mv2com, where M is the total mass and vcom is the velocity of the center of mass 
D) the kinetic energy of the more massive body before the collision 
E) the kinetic energy of the less massive body before the collision

Question 15

A light rope passes over a light frictionless pulley attached to the ceiling.An object with a large mass is tied to one end and an object with a smaller mass is tied to the other end.Starting from rest, the heavier object moves downward, and the lighter object moves upward with an acceleration of the same magnitude.Which of the following statements is true for the system consisting of the two objects?

Accepted Answer

A) The center of mass remains at rest. 
B) The net external force is zero. 
C) The velocity of the center of mass is a constant. 
D) The acceleration of the center of mass is g, downward. 
E) None of the above statements are true. 
A) The center of mass remains at rest. 
B) The net external force is zero. 
C) The velocity of the center of mass is a constant. 
D) The acceleration of the center of mass is g, downward. 
E) None of the above statements are true.

Question 16

A man sits in the back of a canoe in still water.He then moves to the front of the canoe and sits there.Afterwards the canoe:

Accepted Answer

A) is forward of its original position and moving forward 
B) is forward of its original position and moving backward 
C) is rearward of its original position and moving forward 
D) is rearward of its original position and moving backward 
E) is rearward of its original position and not moving 
A) is forward of its original position and moving forward 
B) is forward of its original position and moving backward 
C) is rearward of its original position and moving forward 
D) is rearward of its original position and moving backward 
E) is rearward of its original position and not moving

Question 17

A machinist starts with three identical square plates but cuts one corner from one of them, two corners from the second, and three corners from the third.Rank the three plates according to the x coordinates of their centers of mass, from smallest to largest.

Accepted Answer

A) 1, 2, 3 
B) 1 and 2 tie, then 3 
C) 1, then 2 and 3 tie 
D) 3, 2, 1 
E) 1, 3, 2 
A) 1, 2, 3 
B) 1 and 2 tie, then 3 
C) 1, then 2 and 3 tie 
D) 3, 2, 1 
E) 1, 3, 2

Question 18

Two objects, P and Q, have the same momentum.Q can have more kinetic energy than P if it:

Accepted Answer

A) weighs more than P 
B) is moving faster than P 
C) weighs the same as P 
D) is moving slower than P 
E) is moving at the same speed as P 
A) weighs more than P 
B) is moving faster than P 
C) weighs the same as P 
D) is moving slower than P 
E) is moving at the same speed as P

Question 19

A 2-kg cart, traveling on a horizontal air track with a speed of 3 m/s, collides with a stationary 4-kg cart.The carts stick together.The impulse exerted by one cart on the other has a magnitude of:

Accepted Answer

A) 0 N∙s 
B) 4 N∙s 
C) 6 N∙s 
D) 9 N∙s 
E) 12 N∙s 
A) 0 N∙s 
B) 4 N∙s 
C) 6 N∙s 
D) 9 N∙s 
E) 12 N∙s

Question 20

A 500-kg sack of coal is dropped on a 2000-kg railroad flatcar which was initially moving at 3 m/s as shown.After the sack rests on the flatcar, the speed of the flatcar is:

Accepted Answer

A) 0.6 m/s 
B) 1.2 m/s 
C) 1.8 m/s 
D) 2.4 m/s 
E) 3.6 m/s 
A) 0.6 m/s 
B) 1.2 m/s 
C) 1.8 m/s 
D) 2.4 m/s 
E) 3.6 m/s

Exam 9: Center of Mass and Linear Momentum

A 1.0 kg-ball moving at 2.0 m/s perpendicular to a wall rebounds from the wall at 1.5 m/s.The change in the momentum of the ball is:

Two spacemen are floating together with zero speed in a gravity-free region of space.The mass of spaceman A is 120 kg and that of spaceman B is 90 kg.Spaceman A pushes B away from him with B attaining a final speed of 0.5 m/s.The final recoil speed of A is:

Blocks A and B are moving toward each other.A has a mass of 2.0 kg and a velocity of 50 m/s, while B has a mass of 4.0 kg and a velocity of -25 m/s.They suffer a completely inelastic collision.The kinetic energy lost during the collision is:

Which one of the following statements is true?

The center of mass of Earth's atmosphere is:

Force:

The momentum of a system of particles is changing at the rate of 0.71 t + 1.2 t2, in kg∙m/s.The net force at t = 2.0 s

Cart A, with a mass of 0.2 kg, travels on a horizontal air track at 3 m/s and hits cart B, which has a mass of 0.4 kg and is initially at rest.After the collision the center of mass of the two cart system has a speed in m/s of:

A 64-kg woman stands on frictionless level ice with a 0.10-kg stone at her feet.She kicks the stone with her foot so that she acquires a velocity of 0.0017 m/s in the forward direction.The velocity acquired by the stone is:

The momentum of an object at a given instant is independent of its:

A particle moves along the x axis.Its momentum is graphed below as a function of time.Rank the numbered regions according to the magnitude of the force acting on the particle, least to greatest.

Sphere X, of mass 2 kg, is moving to the right at 10 m/s.Sphere Y, of mass 4 kg, is moving to the left at 10 m/s.The two spheres collide head-on.The magnitude of the impulse of X on Y is:

A thick uniform wire is bent into the shape of the letter "U" as shown.Which point indicates the location of the center of mass of this wire?

For a completely inelastic two-body collision the kinetic energy retained by the objects is the same as:

A man sits in the back of a canoe in still water.He then moves to the front of the canoe and sits there.Afterwards the canoe:

A machinist starts with three identical square plates but cuts one corner from one of them, two corners from the second, and three corners from the third.Rank the three plates according to the x coordinates of their centers of mass, from smallest to largest.

Two objects, P and Q, have the same momentum.Q can have more kinetic energy than P if it:

A 2-kg cart, traveling on a horizontal air track with a speed of 3 m/s, collides with a stationary 4-kg cart.The carts stick together.The impulse exerted by one cart on the other has a magnitude of:

A 500-kg sack of coal is dropped on a 2000-kg railroad flatcar which was initially moving at 3 m/s as shown.After the sack rests on the flatcar, the speed of the flatcar is:

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The momentum of a system of particles is changing at the rate of 0.71 t + 1.2 t², in kg∙m/s.The net force at t = 2.0 s