Question 1

When you step on the accelerator to increase the speed of your car, the force that accelerates the car is:

Accepted Answer

A) the force of your foot on the accelerator 
B) the force of friction of the road on the tires 
C) the force of the engine on the drive shaft 
D) the normal force of the road on the tires 
E) none of the above 
A) the force of your foot on the accelerator 
B) the force of friction of the road on the tires 
C) the force of the engine on the drive shaft 
D) the normal force of the road on the tires 
E) none of the above

Question 2

A 10-kg block of ice is at rest on a frictionless horizontal surface.A 1.0-N force is applied in an easterly direction for 1.0 s.During this time interval, the block:

Accepted Answer

A) acquires a speed of 1 m/s 
B) moves 10 cm 
C) acquires a momentum of 1.0 kg .m/s 
D) acquires a kinetic energy of 0.1 J 
E) none of the above 
A) acquires a speed of 1 m/s 
B) moves 10 cm 
C) acquires a momentum of 1.0 kg .m/s 
D) acquires a kinetic energy of 0.1 J 
E) none of the above

Question 3

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 4

The velocity of the center of mass of a system of particles changes as v = 4.5 t + 2.4 t2 + 1.1 t3, where v is in meters per second.If the system starts from rest at t = 0, what is its position at t = 3.0 s?

Accepted Answer

A) 7.1 m 
B) 21 m 
C) 40 m 
D) 49 m 
E) 64 m 
A) 7.1 m 
B) 21 m 
C) 40 m 
D) 49 m 
E) 64 m

Question 5

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 6

If a projectile hits a stationary target, and the projectile stops while the target moves at the same speed as the incoming speed of the projectile,

Accepted Answer

A) the mass of the projectile is much less than the mass of the target. 
B) the mass of the projectile is equal to the mass of the target. 
C) the mass of the projectile is much greater than the mass of the target. 
D) nothing can be said about the masses of the projectile and target without further information. 
E) this is an unphysical situation and will not actually happen. 
A) the mass of the projectile is much less than the mass of the target. 
B) the mass of the projectile is equal to the mass of the target. 
C) the mass of the projectile is much greater than the mass of the target. 
D) nothing can be said about the masses of the projectile and target without further information. 
E) this is an unphysical situation and will not actually happen.

Question 7

A 4.0-N puck is traveling at 3.0 m/s.It strikes an 8.0-N puck, which is stationary.The two pucks stick together.Their common final speed is:

Accepted Answer

A) 1.0 m/s 
B) 1.5 m/s 
C) 2.0 m/s 
D) 2.3 m/s 
E) 3.0 m/s 
A) 1.0 m/s 
B) 1.5 m/s 
C) 2.0 m/s 
D) 2.3 m/s 
E) 3.0 m/s

Question 8

A 2.0-kg block is attached to one end of a spring with a spring constant of 100 N/m and a 4.0-kg block is attached to the other end.The blocks are placed on a horizontal frictionless surface and set into motion.At one instant the 2.0-kg block is observed to be traveling to the right with a speed of 0.50 m/s and the 4.0-kg block is observed to be traveling to the left with a speed of 0.30 m/s.Since the only forces on the blocks are the force of gravity, the normal force of the surface, and the force of the spring, we conclude that:

Accepted Answer

A) the spring is compressed at the time of the observation 
B) the spring is not compressed at the time of observation 
C) the motion was started with the masses at rest 
D) the motion was started with at least one of masses moving 
E) the motion was started by compressing the spring 
A) the spring is compressed at the time of the observation 
B) the spring is not compressed at the time of observation 
C) the motion was started with the masses at rest 
D) the motion was started with at least one of masses moving 
E) the motion was started by compressing the spring

Question 9

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 10

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 11

An elastic 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) kinetic energy and momentum are both 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) kinetic energy and momentum are both conserved 
D) momentum is conserved but kinetic energy is not conserved 
E) the total impulse is equal to the change in kinetic energy

Question 12

A cart loaded with sand slides forward along a horizontal frictionless track.As the cart moves, sand trickles out at a constant rate through a hole in the back of the cart.The acceleration of the cart is:

Accepted Answer

A) constant and in the forward direction 
B) constant and in the backward direction 
C) variable and in the forward direction 
D) variable and in the backward direction 
E) zero 
A) constant and in the forward direction 
B) constant and in the backward direction 
C) variable and in the forward direction 
D) variable and in the backward direction 
E) zero

Question 13

What magnitude impulse will give a 2.0-kg object a momentum change of magnitude +50 kg∙m/s?

Accepted Answer

A) + 25 N∙s 
B) - 25 N∙s 
C) + 50 N∙s 
D) - 50 N∙s 
E) + 100 N∙s 
A) + 25 N∙s 
B) - 25 N∙s 
C) + 50 N∙s 
D) - 50 N∙s 
E) + 100 N∙s

Question 14

Two identical carts travel at 1 m/s on a common surface.They collide head-on and are reported to rebound, each with a speed of 2 m/s.Then:

Accepted Answer

A) momentum was not conserved, therefore the report must be false 
B) if some other form of energy were changed to kinetic during the collision, the report could be true 
C) if the collision were elastic, the report could be true 
D) if the surface were inclined, the report could be true 
E) kinetic energy increased, therefore the report must be false 
A) momentum was not conserved, therefore the report must be false 
B) if some other form of energy were changed to kinetic during the collision, the report could be true 
C) if the collision were elastic, the report could be true 
D) if the surface were inclined, the report could be true 
E) kinetic energy increased, therefore the report must be false

Question 15

The center of mass of a system of particles has a constant velocity if:

Accepted Answer

A) the forces exerted by the particles on each other sum to zero 
B) the external forces acting on particles of the system sum to zero 
C) the velocity of the center of mass is initially zero 
D) the particles are distributed symmetrically around the center of mass 
E) the center of mass is at the geometric center of the system 
A) the forces exerted by the particles on each other sum to zero 
B) the external forces acting on particles of the system sum to zero 
C) the velocity of the center of mass is initially zero 
D) the particles are distributed symmetrically around the center of mass 
E) the center of mass is at the geometric center of the system

Question 16

A very massive object traveling at 10 m/s strikes a light object, initially at rest, and the light object moves off in the direction of travel of the heavy object.If the collision is elastic, the speed of the lighter object is

Accepted Answer

A) 5.0 m/s 
B) 10 m/s 
C) 15 m/s 
D) 20 m/s 
E) Can't tell from the information given. 
A) 5.0 m/s 
B) 10 m/s 
C) 15 m/s 
D) 20 m/s 
E) Can't tell from the information given.

Question 17

A 2.5-kg stone is released from rest and falls toward Earth.After 4.0 s, the magnitude of its momentum is:

Accepted Answer

A) 98 kg∙m/s 
B) 78 kg∙m/s 
C) 39 kg∙m/s 
D) 24 kg∙m/s 
E) 0 kg∙m/s 
A) 98 kg∙m/s 
B) 78 kg∙m/s 
C) 39 kg∙m/s 
D) 24 kg∙m/s 
E) 0 kg∙m/s

Question 18

In a one-dimensional collision,

Accepted Answer

A) a moving object strikes a stationary object, after which the objects move in arbitrary directions. 
B) the objects must be moving along the same line before the collision, but may be moving in arbitrary directions after the collision. 
C) one of the objects must remain at rest after the collision. 
D) one of the objects must be at rest before the collision. 
E) all motion, both before and after the collision, must be along the same line. 
A) a moving object strikes a stationary object, after which the objects move in arbitrary directions. 
B) the objects must be moving along the same line before the collision, but may be moving in arbitrary directions after the collision. 
C) one of the objects must remain at rest after the collision. 
D) one of the objects must be at rest before the collision. 
E) all motion, both before and after the collision, must be along the same line.

Question 19

The center of mass of a uniform disk of radius R is located:

Accepted Answer

A) on the rim 
B) a distance R/2 from the center 
C) a distance R/3 from the center 
D) a distance 2R/3 from the center 
E) at the center 
A) on the rim 
B) a distance R/2 from the center 
C) a distance R/3 from the center 
D) a distance 2R/3 from the center 
E) at the center

Exam 9: Center of Mass and Linear Momentum

When you step on the accelerator to increase the speed of your car, the force that accelerates the car is:

A 10-kg block of ice is at rest on a frictionless horizontal surface.A 1.0-N force is applied in an easterly direction for 1.0 s.During this time interval, the block:

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:

The velocity of the center of mass of a system of particles changes as v = 4.5 t + 2.4 t2 + 1.1 t3, where v is in meters per second.If the system starts from rest at t = 0, what is its position at t = 3.0 s?

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?

If a projectile hits a stationary target, and the projectile stops while the target moves at the same speed as the incoming speed of the projectile,

A 4.0-N puck is traveling at 3.0 m/s.It strikes an 8.0-N puck, which is stationary.The two pucks stick together.Their common final speed is:

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:

An inelastic collision is one in which:

An elastic collision is one in which:

A cart loaded with sand slides forward along a horizontal frictionless track.As the cart moves, sand trickles out at a constant rate through a hole in the back of the cart.The acceleration of the cart is:

What magnitude impulse will give a 2.0-kg object a momentum change of magnitude +50 kg∙m/s?

Two identical carts travel at 1 m/s on a common surface.They collide head-on and are reported to rebound, each with a speed of 2 m/s.Then:

The center of mass of a system of particles has a constant velocity if:

A very massive object traveling at 10 m/s strikes a light object, initially at rest, and the light object moves off in the direction of travel of the heavy object.If the collision is elastic, the speed of the lighter object is

A 2.5-kg stone is released from rest and falls toward Earth.After 4.0 s, the magnitude of its momentum is:

In a one-dimensional collision,

The center of mass of a uniform disk of radius R is located:

Measurement

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Filters

The velocity of the center of mass of a system of particles changes as v = 4.5 t + 2.4 t² + 1.1 t³, where v is in meters per second.If the system starts from rest at t = 0, what is its position at t = 3.0 s?