Question 1

A hailstone shatters a roof tile, as shown in the study materials. Why is it often more practical to use the concept of momentum rather than Newton’s second law to analyze this event?

Accepted Answer

Because the forces during the collision are complicated and not easily known, but the change in momentum can be determined from initial and final velocities.

Question 2

Which of the following correctly expresses Newton’s second law in terms of momentum?

Accepted Answer

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

Question 3

A 0.40 kg ball is thrown horizontally at 30 m/s to the left and rebounds to the right at 20 m/s after hitting a wall. What is the impulse delivered to the ball by the wall?

Accepted Answer

$$20\ \mathrm{kg \cdot m/s}$$

Question 4

The impulse-momentum theorem states:

Accepted Answer

The impulse of the net external force on a particle during a time interval equals the change in momentum of that particle during that interval.

Question 5

A soccer ball of mass 0.40 kg is moving to the left at 20 m/s. After being kicked, it moves at 30 m/s at a $$45^\circ$$ angle upward and to the right. What is the magnitude of the change in the ball’s momentum?

Accepted Answer

$$20.0\ \mathrm{kg \cdot m/s}$$

Question 6

Why is it safer to land with your knees bent after jumping from a height?

Accepted Answer

Bending your knees increases the time interval over which you stop, decreasing the force.

Question 7

Which of the following is true for an isolated system of two astronauts pushing off each other in space?

Accepted Answer

The total momentum of the system is conserved.

Question 8

A 1000 kg car traveling north at 15 m/s collides with a 2000 kg truck traveling east at 10 m/s. After the collision, the vehicles stick together. What is the magnitude of their velocity just after the collision?

Accepted Answer

$$11.2\ \mathrm{m/s}$$

Question 9

In a perfectly elastic collision between two objects of equal mass, where one is initially at rest, what happens to the velocities after the collision?

Accepted Answer

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

Question 10

A 5.00 g bullet is fired horizontally into a 1.20 kg wooden block resting on a horizontal surface. The bullet embeds in the block, and the block slides 0.310 m before stopping. If the coefficient of kinetic friction is 0.20, what principle is used to find the initial speed of the bullet?

Accepted Answer

Conservation of momentum followed by work-energy principle

Question 11

Which of the following statements about inelastic collisions is correct?

Accepted Answer

Objects stick together in a completely inelastic collision.

Question 12

A marksman fires a 5.00 g bullet at 300 m/s from a 3.00 kg rifle. What is the recoil velocity of the rifle?

Accepted Answer

$$-0.50\ \mathrm{m/s}$$

Question 13

Which of the following best describes the center of mass of a system?

Accepted Answer

It is the point where all the mass of the system can be considered to be concentrated for analyzing translational motion.

Question 14

A system of two particles has momenta $$\vec{p}_A$$ and $$\vec{p}_B in $$different directions. How do you find the total momentum?

Accepted Answer

Use vector addition: $$\vec{p} = \vec{p}_A + \vec{p}_B$$

Question 15

Which of the following is true for the motion of the center of mass of a system acted on by external forces?

Accepted Answer

The center of mass moves as though all the mass were concentrated at that point and acted on by the net external force.

Question 16

In a collision between two cars, why are modern cars designed to crumple and deform rather than remain rigid?

Accepted Answer

To absorb energy and reduce the force experienced by the occupants by increasing the collision time.

Question 17

Which equation correctly gives the position of the center of mass for particles with masses $$m_1$$, $$m_2$$, \ldots$$ at positions $$\vec{r}_1, \vec{r}_2, \ldots$$?

Accepted Answer

$$\vec{R}_{CM} = \frac{\sum m_i \vec{r}_i}{\sum m_i}$$

Momentum, Impulse, and Collisions – Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards