Question 1

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 2

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 3

The center of mass of the system consisting of Earth, the Sun, and the planet Mars is:

Accepted Answer

A)  closer to the Earth than to either of the other bodies 
B)  closer to the Sun than to either of the other bodies 
C)  closer to Mars than to either of the other bodies 
D)  at the geometric center of the triangle formed by the three bodies 
E)  at the center of the line joining the Earth and Mars 
A)  closer to the Earth than to either of the other bodies 
B)  closer to the Sun than to either of the other bodies 
C)  closer to Mars than to either of the other bodies 
D)  at the geometric center of the triangle formed by the three bodies 
E)  at the center of the line joining the Earth and Mars

Question 4

At the same instant that a 0.50-kg ball is dropped from 25 m above Earth, a second ball, with a mass of 0.25 kg, is thrown straight upward from Earth's surface with an initial speed of 15 m/s. They move along nearby lines and pass each other without colliding. At the end of 2.0 s the height above Earth's surface of the center of mass of the two-ball system is:

Accepted Answer

A)  2.9 m 
B)  4.0 m 
C)  7.1 m 
D)  7.9 m 
E)  10.4 m 
A)  2.9 m 
B)  4.0 m 
C)  7.1 m 
D)  7.9 m 
E)  10.4 m

Question 5

A 3.00-g bullet traveling horizontally at 400 m/s hits a 3.00-kg wooden block, which is initially at rest on a smooth horizontal table. The bullet buries itself in the block without passing through. The speed of the block after the collision is:

Accepted Answer

A)  1.33 m/s 
B)  0.40 m/s 
C)  12.0 m/s 
D)  12.6 m/s 
E)  40.0 m/s 
A)  1.33 m/s 
B)  0.40 m/s 
C)  12.0 m/s 
D)  12.6 m/s 
E)  40.0 m/s

Question 6

When a particle suffers a head-on elastic collision with another particle, initially at rest, the greatest fraction of kinetic energy is transferred if:

Accepted Answer

A)  the incident particle is initially traveling very fast 
B)  the incident particle is traveling very slowly 
C)  the incident particle is much more massive than the target particle 
D)  the incident particle is much less massive than the target particle 
E)  the incident and target particle have the same mass 
A)  the incident particle is initially traveling very fast 
B)  the incident particle is traveling very slowly 
C)  the incident particle is much more massive than the target particle 
D)  the incident particle is much less massive than the target particle 
E)  the incident and target particle have the same mass

Question 7

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

Question 8

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 9

A projectile in flight explodes into several fragments. The total momentum of the fragments immediately after this explosion:

Accepted Answer

A)  is the same as the momentum of the projectile immediately before the explosion 
B)  has been changed into kinetic energy of the fragments 
C)  is less than the momentum of the projectile immediately before the explosion 
D)  is more than the momentum of the projectile immediately before the explosion 
E)  has been changed into radiant energy 
A)  is the same as the momentum of the projectile immediately before the explosion 
B)  has been changed into kinetic energy of the fragments 
C)  is less than the momentum of the projectile immediately before the explosion 
D)  is more than the momentum of the projectile immediately before the explosion 
E)  has been changed into radiant energy

Question 10

Object A strikes the stationary object B head-on in an elastic collision. The mass of A is fixed, you may choose the mass of B appropriately. Then:

Accepted Answer

A)  for B to have the greatest recoil speed, choose mB = mA 
B)  for B to have the greatest recoil momentum, choose mB A 
C)  for B to have the greatest recoil kinetic energy, choose mB >> mA 
D)  for B to have the least recoil speed, choose mB = mA 
E)  for B to have the greatest recoil kinetic energy, choose mB = mA 
A)  for B to have the greatest recoil speed, choose mB = mA 
B)  for B to have the greatest recoil momentum, choose mB A 
C)  for B to have the greatest recoil kinetic energy, choose mB >> mA 
D)  for B to have the least recoil speed, choose mB = mA 
E)  for B to have the greatest recoil kinetic energy, choose mB = mA

Question 11

A hockey puck of mass m traveling along the x axis at 4.5 m/s hits another identical hockey puck at rest. If after the collision the second puck travels at a speed of 3.5 m/s at an angle of 30° above the x axis, what is the final velocity of the first puck?

Accepted Answer

A)  1.0 m/s, 30° below the x axis 
B)  2.3 m/s, 50° below the x axis 
C)  2.8 m/s, 60° below the x axis 
D)  3.0 m/s, 45° below the x axis 
E)  not enough information 
A)  1.0 m/s, 30° below the x axis 
B)  2.3 m/s, 50° below the x axis 
C)  2.8 m/s, 60° below the x axis 
D)  3.0 m/s, 45° below the x axis 
E)  not enough information

Question 12

Bullets from two revolvers are fired with the same velocity. The bullet from gun #1 is twice as heavy as the bullet from gun #2. Gun #1 weighs three times as much as gun #2. The ratio of the momentum imparted to gun #1 to that imparted to gun #2 is:

Accepted Answer

A)  2:3 
B)  3:2 
C)  2:1 
D)  3:1 
E)  6:1 
A)  2:3 
B)  3:2 
C)  2:1 
D)  3:1 
E)  6:1

Question 13

An inelastic collision is one in which:

Accepted Answer

A)  momentum is not conserved but kinetic energy is conserved 
B)  total mass is not conserved but momentum is conserved 
C)  neither kinetic energy nor momentum is conserved 
D)  momentum is conserved but kinetic energy is not conserved 
E)  the total impulse is equal to the change in kinetic energy 
A)  momentum is not conserved but kinetic energy is conserved 
B)  total mass is not conserved but momentum is conserved 
C)  neither kinetic energy nor momentum is conserved 
D)  momentum is conserved but kinetic energy is not conserved 
E)  the total impulse is equal to the change in kinetic energy

Question 14

A 3.0-kg cart and a 2.0-kg cart approach each other on a horizontal air track. They collide and stick together. After the collision their total kinetic energy is 40 J. The speed of their center of mass is:

Accepted Answer

A)  0 m/s 
B)  2.8 m/s 
C)  4.0 m/s 
D)  5.2 m/s 
E)  8.0 m/s 
A)  0 m/s 
B)  2.8 m/s 
C)  4.0 m/s 
D)  5.2 m/s 
E)  8.0 m/s

Question 15

A hockey puck of mass m traveling along the x axis at 4.5 m/s hits another identical hockey puck at rest. If after the collision the second puck travels at a speed of 3.5 m/s at an angle of 30° above the x axis, is this an elastic collision?

Accepted Answer

A)  Yes, since momentum is conserved. 
B)  No, since momentum is not conserved. 
C)  Yes, since kinetic energy is conserved. 
D)  No, since kinetic energy is not conserved. 
E)  Not enough information. 
A)  Yes, since momentum is conserved. 
B)  No, since momentum is not conserved. 
C)  Yes, since kinetic energy is conserved. 
D)  No, since kinetic energy is not conserved. 
E)  Not enough information.

Question 16

The acceleration of the center of mass of a system of particles:

Accepted Answer

A)  depends on all the forces on all the particles 
B)  depends on all the velocities of all the particles 
C)  depends only on the forces external to the system of particles 
D)  depends only on the forces internal to the system of particles 
E)  depends only on the force of gravity 
A)  depends on all the forces on all the particles 
B)  depends on all the velocities of all the particles 
C)  depends only on the forces external to the system of particles 
D)  depends only on the forces internal to the system of particles 
E)  depends only on the force of gravity

Question 17

A 640-N acrobat falls 5.0 m from rest into a net. The net tosses him back up with the same speed he had just before he hit the net. The average upward force exerted on him by the net during this collision is:

Accepted Answer

A)  32 N 
B)  64 N 
C)  320 N 
D)  640 N 
E)  impossible to determine from given data 
A)  32 N 
B)  64 N 
C)  320 N 
D)  640 N 
E)  impossible to determine from given data

Question 18

The physical quantity "impulse" has the same dimensions as that of:

Accepted Answer

A)  force 
B)  power 
C)  energy 
D)  momentum 
E)  work 
A)  force 
B)  power 
C)  energy 
D)  momentum 
E)  work

Question 19

The thrust of a rocket is

Accepted Answer

A)  a gravitational force acting on the rocket 
B)  the force of the exiting fuel gases on the rocket 
C)  any force that is external to the rocket-fuel system 
D)  a force that arises from the reduction in mass of the rocket-fuel system 
E)  none of the above 
A)  a gravitational force acting on the rocket 
B)  the force of the exiting fuel gases on the rocket 
C)  any force that is external to the rocket-fuel system 
D)  a force that arises from the reduction in mass of the rocket-fuel system 
E)  none of the above

Exam 9: Center of Mass and Linear Momentum

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.

The center of mass of the system consisting of Earth, the Sun, and the planet Mars is:

A 3.00-g bullet traveling horizontally at 400 m/s hits a 3.00-kg wooden block, which is initially at rest on a smooth horizontal table. The bullet buries itself in the block without passing through. The speed of the block after the collision is:

When a particle suffers a head-on elastic collision with another particle, initially at rest, the greatest fraction of kinetic energy is transferred if:

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:

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

A projectile in flight explodes into several fragments. The total momentum of the fragments immediately after this explosion:

Object A strikes the stationary object B head-on in an elastic collision. The mass of A is fixed, you may choose the mass of B appropriately. Then:

A hockey puck of mass m traveling along the x axis at 4.5 m/s hits another identical hockey puck at rest. If after the collision the second puck travels at a speed of 3.5 m/s at an angle of 30° above the x axis, what is the final velocity of the first puck?

Bullets from two revolvers are fired with the same velocity. The bullet from gun #1 is twice as heavy as the bullet from gun #2. Gun #1 weighs three times as much as gun #2. The ratio of the momentum imparted to gun #1 to that imparted to gun #2 is:

An inelastic collision is one in which:

A 3.0-kg cart and a 2.0-kg cart approach each other on a horizontal air track. They collide and stick together. After the collision their total kinetic energy is 40 J. The speed of their center of mass is:

A hockey puck of mass m traveling along the x axis at 4.5 m/s hits another identical hockey puck at rest. If after the collision the second puck travels at a speed of 3.5 m/s at an angle of 30° above the x axis, is this an elastic collision?

The acceleration of the center of mass of a system of particles:

A 640-N acrobat falls 5.0 m from rest into a net. The net tosses him back up with the same speed he had just before he hit the net. The average upward force exerted on him by the net during this collision is:

The physical quantity "impulse" has the same dimensions as that of:

The thrust of a rocket 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