Q: A 0.15 kg baseball is pitched at 20 m/s toward a batter and is hit straight back at 40 m/s. If the contact time between the bat and the ball is 0.0030 s, what is the magnitude of the average force exerted by the bat on the ball?

$$F_{\text{avg}} = 300\ \text{N}$$

Q: A 0.2 kg glider moving at 3.0 m/s to the right collides and sticks to a 0.4 kg glider. After the collision, the combined gliders move to the left at 0.40 m/s. What was the initial velocity of the 0.4 kg glider?

$$v = 2.1\ \text{m/s}$$\ to\ the\ left

Q: A 600 g javelin is thrown at 25 m/s by a 55 kg athlete standing on a 2.0 kg skateboard. What is the recoil speed of the athlete and skateboard immediately after the throw?

$$v = 0.26\ \text{m/s}$$\ to\ the\ left

Question 1

A 0.15 kg baseball is pitched at 20 m/s toward a batter and is hit straight back at 40 m/s. If the contact time between the bat and the ball is 0.0030 s, what is the magnitude of the average force exerted by the bat on the ball?

Accepted Answer

$$F_{	ext{avg}} = 300\ 	ext{N}$$

Question 2

Which of the following statements about momentum is correct?

Accepted Answer

Momentum is a vector quantity and depends on both the magnitude and direction of velocity.

Question 3

A 75 kg person runs at 4 m/s and jumps onto a stationary 25 kg cart. What is the speed of the person and cart immediately after the collision?

Accepted Answer

$$v = 3.0\ 	ext{m/s}$$

Question 4

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

Accepted Answer

Momentum is conserved, but kinetic energy is not.

Question 5

A 0.2 kg glider moving at 3.0 m/s to the right collides and sticks to a 0.4 kg glider. After the collision, the combined gliders move to the left at 0.40 m/s. What was the initial velocity of the 0.4 kg glider?

Accepted Answer

$$v = 2.1\ 	ext{m/s}$$\ to\ the\ left

Question 6

A 600 g javelin is thrown at 25 m/s by a 55 kg athlete standing on a 2.0 kg skateboard. What is the recoil speed of the athlete and skateboard immediately after the throw?

Accepted Answer

$$v = 0.26\ 	ext{m/s}$$\ to\ the\ left

Question 7

Which of the following best describes an isolated system in the context of momentum conservation?

Accepted Answer

A system in which the net external force is zero.

Question 8

A 200 g ball moving at 2.0 m/s to the right collides head-on with a 100 g ball moving at 3.0 m/s to the left. The collision is perfectly elastic. What is the velocity of the 200 g ball after the collision?

Accepted Answer

$$v = -0.33\ 	ext{m/s}$$

Question 9

Which of the following is the correct mathematical expression for impulse $$J$$ delivered by a force $$F(t)$$ over a time interval $$\Delta t$$?

Accepted Answer

$$J = \int_{t_0$}^{t_0$+\Delta t} F(t)\,dt$$

Question 10

A rocket in deep space has a launch mass of 290 kg and burns 210 kg of fuel, generating a constant thrust of 49 kN for 9.0 s. If the exhaust velocity is $$v_e$$, what is the rocket's maximum speed after burning all its fuel?

Accepted Answer

$$v = v_e \ln \left( \frac{290}{80} \right)$$

Question 11

In a perfectly elastic head-on collision between two identical masses, one at rest and one moving, what happens to their velocities after the collision?

Accepted Answer

The moving mass stops and the stationary mass moves with the initial velocity of the first.

Question 12

A rubber ball of mass $$m is $$dropped and bounces off the ground. If the ball is considered as the system, is momentum conserved during the collision with the ground?

Accepted Answer

No, because the ground exerts an external force on the ball.

Question 13

Which of the following best describes the difference between an explosion and a collision in terms of momentum?

Accepted Answer

In an explosion, objects start together and move apart; in a collision, objects start apart and may stick together or bounce off.

Question 14

A 0.5 kg ball moving at 4 m/s collides elastically with a stationary 0.5 kg ball. What is the velocity of the first ball after the collision?

Accepted Answer

$$v = 0\ 	ext{m/s}$$

Question 15

A force $$F(t)$$ acts on a particle for a short time interval $$\Delta t. $$Which of the following statements is correct regarding the impulse delivered to the particle?

Accepted Answer

The impulse is equal to the area under the force vs. time graph.

Question 16

A 2 kg object moving at 5 m/s collides with a 3 kg object at rest. If the collision is perfectly inelastic, what is their common velocity after the collision?

Accepted Answer

$$v = 2\ 	ext{m/s}$$

Question 17

Which of the following is a correct statement of the law of conservation of momentum for an isolated system?

Accepted Answer

$$\sum \vec{p}_{	ext{initial}} = \sum \vec{p}_{	ext{final}}$$

Question 18

A rocket expels exhaust gases at a constant rate with speed $$v_e$$ relative to the rocket. If the rocket's mass decreases from $$m_0 to$$ $$m_f as it $$burns fuel, what is the change in the rocket's velocity?

Accepted Answer

$$\Delta v = v_e \ln \left( \frac{m_0$}{m_f} \right)$$

Impulse and Momentum: Study Notes (Physics for Scientists and Engineers, Ch. 11)

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