Question 1

A supertanker and a Honda Civic are both moving at the same speed. Which of the following best explains why the supertanker is harder to stop than the Honda Civic?

Accepted Answer

The supertanker has a larger mass, so its momentum $$p = mv is $$much greater.

Question 2

Which equation correctly expresses Newton's second law in terms of momentum?

Accepted Answer

$$\sum \vec{F} = \dfrac{d\vec{p}}{dt}$$

Question 3

A golf ball is struck by a club, and the force exerted by the club on the ball varies over the time of contact. What does the area under the force vs. time curve represent?

Accepted Answer

The impulse delivered to the ball

Question 4

A truck with mass $$m$$ and velocity $$v is $$brought to a stop by crashing into a large bale of hay or a concrete wall. If the impulse is the same in both cases, which scenario results in a larger average force on the truck?

Accepted Answer

Crashing into the concrete wall, because the stopping time is much shorter.

Question 5

Which of the following best describes the law of conservation of momentum for a system of two colliding objects, A and B, in the absence of external forces?

Accepted Answer

$$m_A \vec{v}_A + m_B \vec{v}_B = m_A \vec{v}'_A + m_B \vec{v}'_B$$

Question 6

A rifle of mass $$m_R$$ fires a bullet of mass $$m_b. If $$the bullet leaves the rifle with velocity $$v$$, what is the recoil velocity of the rifle?

Accepted Answer

$$v_R = -\dfrac{m_b}{m_R} v$$

Question 7

Which of the following statements about impulse is correct?

Accepted Answer

Impulse is equal to the change in momentum: $$J = \Delta p$$

Question 8

A cannon fires a cannonball. Why does a longer barrel allow the cannonball to reach a higher speed?

Accepted Answer

The force acts over a longer time, increasing the impulse and thus the momentum.

Question 9

In a collision between two objects, the forces they exert on each other are:

Accepted Answer

Equal in magnitude and opposite in direction, according to Newton's third law.

Question 10

A ball of mass $$m is $$dropped from a height and lands on a pillow, coming to rest. Compared to landing on concrete, why does landing on a pillow hurt less?

Accepted Answer

The pillow increases the stopping time, reducing the average force exerted on the ball.

Question 11

Which of the following is a correct definition of momentum?

Accepted Answer

Momentum is the product of an object's mass and velocity: $$\vec{p} = m\vec{v}$$

Question 12

If the net external force on a system is zero, what happens to the total momentum of the system?

Accepted Answer

It remains constant.

Question 13

A baseball of mass $$0.15\ \mathrm{kg} is $$hit by a bat, changing its velocity from $$-40\ \mathrm{m/s} to$$ $$50\ \mathrm{m/s} in$$ $$0.005\ \mathrm{s}. $$What is the average force exerted by the bat?

Accepted Answer

$$F_{avg} = \dfrac{m(v_f - v_i)}{\Delta t} = \dfrac{0.15 	imes (50 - (-40))}{0.005} = 2700\ \mathrm{N}$$

Question 14

Which of the following is NOT a requirement for the law of conservation of momentum to hold in a system?

Accepted Answer

The system must be at rest before the interaction.

Question 15

A soccer ball of mass $$0.45\ \mathrm{kg} is $$kicked and receives an impulse of $$9\ \mathrm{N \cdot s}. $$What is the change in velocity of the ball?

Accepted Answer

$$\Delta v = \dfrac{J}{m} = \dfrac{9}{0.45} = 20\ \mathrm{m/s}$$

Question 16

During a collision, two ice skaters push off from each other. If skater A has twice the mass of skater B, what is true about their velocities after the push?

Accepted Answer

Skater B will have twice the velocity of skater A in the opposite direction.

Question 17

Which of the following real-world scenarios best illustrates the concept of impulse?

Accepted Answer

A tennis player follows through with their swing to increase the time of contact with the ball.

Question 18

A system consists of two objects, A and B, with masses $$m_A$$ and $$m_B. If no $$external forces act, and they collide elastically, which quantity is conserved?

Accepted Answer

Both momentum and kinetic energy

Question 19

A ball of mass $$m$$ moving at velocity $$v$$ collides with a stationary ball of equal mass in a perfectly elastic head-on collision. What are their velocities after the collision?

Accepted Answer

The moving ball comes to rest, and the stationary ball moves with velocity $$v.$$

M05_Momentum, Impulse, and Conservation Laws in Physics

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