Q: A tennis ball of mass $$6.0 \times 10$$^{-2}$$ kg and speed 33$ m/s strikes a wall at a 45$$^{\circ}$$ angle and rebounds with the same speed and angle. What is the magnitude of the impulse delivered to the ball?

$$p = 2.8 kg$$·m/s \ (\text{to two significant figures})

Q: Two cars, each of mass $$m$$, collide and stick together. Before the collision, one car travels east at $$2v$$ and the other north at $$v. $$What is the speed of the joined cars after the collision?

$$v_{\text{final}} = \sqrt{5}v/2$$

Q: A neutron collides elastically with a stationary helium nucleus (mass four times that of the neutron). If the neutron's initial speed is $$3.0 \times 10^5$ m/s and the helium nucleus moves off at 45$$^{\circ}$$ after the collision, what is the speed of the neutron after the collision?

$$v_{n,f} = 2.4 \times 10^5$ m/s

Q: A tennis ball of mass $$m$$ and speed $$v$$ strikes a wall at an angle $$\theta$$ and rebounds with the same speed and angle. What is the change in the $$x-$$component of the ball's momentum?

$$\Delta p_x = 2mv \cos \theta$$

Question 1

A lump of putty and a rubber ball, each of mass $$m$$, are thrown with equal speed $$v$$ against a wall. The putty sticks to the wall, while the ball bounces back with the same speed. Which object experiences the greater magnitude of momentum change?

Accepted Answer

The ball experiences the greater momentum change.

Question 2

A 0.249 kg puck A slides on a frictionless table toward puck B (0.375 kg) at rest. After the collision, puck A moves at $$-0.125 m/s $$and puck B at $$0.652 m/s. $$What was the initial speed of puck A before the collision?

Accepted Answer

$$v_{A,i} = 1.02 m/s$$

Question 3

A 0.130-kg baseball pitched at $$31.5 m/s is $$hit back at $$57.0 m/s. If $$the contact time is $$6.05 	imes 10$$^{-4}$$ s, what is the magnitude of the average force exerted on the ball?

Accepted Answer

$$F = 1.90 	imes 10$$^{4}$$ N

Question 4

A tennis ball of mass $$6.0 	imes 10$$^{-2}$$ kg and speed 33$ m/s strikes a wall at a 45$$^{\circ}$$ angle and rebounds with the same speed and angle. What is the magnitude of the impulse delivered to the ball?

Accepted Answer

$$p = 2.8 kg$$·m/s \ (	ext{to two significant figures})

Question 5

Two cars, each of mass $$m$$, collide and stick together. Before the collision, one car travels east at $$2v$$ and the other north at $$v. $$What is the speed of the joined cars after the collision?

Accepted Answer

$$v_{	ext{final}} = \sqrt{5}v/2$$

Question 6

A 0.485-kg hockey puck moving east at $$4.35 m/s $$collides head-on with a 0.760-kg puck at rest. Assuming a perfectly elastic collision, what is the speed of the lighter puck after the collision?

Accepted Answer

$$v = -1.67 m/s$

Question 7

A bullet of mass $$0.016 kg $$embeds itself in a wooden block of mass $$0.981 kg$$, compressing a spring ($$k = 160 N/m) by$$ $$0.060 m $$before coming to rest. What was the initial speed of the bullet?

Accepted Answer

$$v = 33.5 m/s$$

Question 8

A neutron collides elastically with a stationary helium nucleus (mass four times that of the neutron). If the neutron's initial speed is $$3.0 	imes 10^5$ m/s and the helium nucleus moves off at 45$$^{\circ}$$ after the collision, what is the speed of the neutron after the collision?

Accepted Answer

$$v_{n,f} = 2.4 	imes 10^5$ m/s

Question 9

A spherical asteroid has a mass of $$3500 kg $$per cubic meter of volume and moves toward Earth at $$14 km/s. If it $$has a volume of $$1.0 	imes 10^9$ m^3$, how much kinetic energy is released when it embeds itself in the Earth?

Accepted Answer

$$E = 3.4 	imes 10$$^{18}$$ J

Question 10

A ball of mass $$m$$ moving with velocity $$v_i$$ strikes a vertical wall and rebounds elastically. What is the change in the ball's momentum?

Accepted Answer

$$\Delta p = 2mv_i$$

Question 11

In a perfectly inelastic collision, which of the following is always true?

Accepted Answer

Momentum is conserved.

Question 12

A 0.485-kg hockey puck moving east at $$4.35 m/s $$collides head-on with a 0.760-kg puck at rest. After a perfectly elastic collision, what is the direction of the heavier puck?

Accepted Answer

East

Question 13

A tennis ball of mass $$m$$ strikes a wall at $$45^{\circ}$$ and rebounds with the same speed. What is the direction of the impulse given to the ball?

Accepted Answer

The impulse is directed horizontally away from the wall.

Question 14

A bullet of mass $$m$$ embeds itself in a block of mass $$M$$ resting on a frictionless surface. If the bullet's initial speed is $$v_0$$, what is the final speed of the block and bullet together?

Accepted Answer

$$v_f = \frac{m}{m+M} v_0$

Question 15

In a collision between two objects, which of the following statements is always true?

Accepted Answer

The total momentum of the system is conserved.

Question 16

A car of mass $$m$$ traveling at speed $$v$$ collides with a stationary truck of mass $$2m. If $$the collision is perfectly inelastic, what is the final speed of the combined mass?

Accepted Answer

$$v_f = \frac{1}{3}v$$

Question 17

A neutron collides elastically with a stationary helium nucleus (mass $$4m). If $$the neutron is scattered at $$90^{\circ}$$, what is the speed of the helium nucleus after the collision?

Accepted Answer

$$v_{He} = \frac{2}{\sqrt{5}}v_{n,i}$$

Question 18

A 0.016-kg bullet embeds itself in a 0.981-kg block, compressing a spring by 0.060 m ($$k = 160 N/m). $$What fraction of the bullet's initial kinetic energy is dissipated in the collision?

Accepted Answer

$$\Delta K / K = 0.85$$

Question 19

A tennis ball of mass $$m$$ and speed $$v$$ strikes a wall at an angle $$	heta$$ and rebounds with the same speed and angle. What is the change in the $$x-$$component of the ball's momentum?

Accepted Answer

$$\Delta p_x = 2mv \cos 	heta$$

Collisions and Momentum in Physics: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards