Question 1

Which of the following best describes the center of mass (CM) of a system?

Accepted Answer

The unique point at which the weighted relative positions of all masses are balanced in all directions.

Question 2

Given three particles located at positions $$x_1 = 1.2$$\ \mathrm{m}$$, x_2$ = 2.0\ \mathrm{m}$$, and $$x_3 = 5.0$$\ \mathrm{m}$$ with masses m_1$ = 3.0\ \mathrm{kg}$$, $$m_2 = 4.0$$\ \mathrm{kg}$$, and m_3$ = 5.0\ \mathrm{kg}$$, what is the $$x-$$coordinate of the center of mass?

Accepted Answer

$$x_{CM} = 3.2\ \mathrm{m}$$

Question 3

A bullet of mass $$5.0 	imes 10$$^{-3}$$\ \mathrm{kg}$$ traveling at $$900\ \mathrm{m/s}$$ has a momentum of $$4.5\ \mathrm{kg\cdot m/s}. $$What is the formula for momentum?

Accepted Answer

$$p = m 	imes v$$

Question 4

Which of the following statements about elastic collisions is correct?

Accepted Answer

Both momentum and kinetic energy are conserved.

Question 5

In a perfectly inelastic collision, which of the following occurs?

Accepted Answer

The colliding objects stick together and move as one mass after the collision.

Question 6

A $$10\ \mathrm{kg}$$ object moving at $$4.0\ \mathrm{m/s}$$ bounces back in the opposite direction at $$2.0\ \mathrm{m/s}. $$What is the change in momentum?

Accepted Answer

Question 7

Which equation expresses the impulse delivered to an object?

Accepted Answer

$$J = F \cdot t$$

Question 8

A $$20\ \mathrm{g}$$ bullet fired at $$900\ \mathrm{m/s}$$ from a $$4.5\ \mathrm{kg}$$ gun. If the gun recoils at $$0.25\ \mathrm{m/s}$$, what is the momentum of the gun after firing?

Accepted Answer

$$p = 1.125\ \mathrm{kg\cdot m/s}$$

Question 9

Which of the following is true about inelastic collisions?

Accepted Answer

Momentum is conserved, but kinetic energy is not.

Question 10

Two billiard balls of equal mass $$m$$ collide head-on with velocities $$v_1$$ and $$v_2. $$After an elastic collision, what are their final velocities?

Accepted Answer

$$v_{1f} = v_2$, v$$_{2f} = $$v_1$$

Question 11

A $$150\ \mathrm{kg}$$ football player running north at $$6.0\ \mathrm{m/s}$$ collides with a $$100\ \mathrm{kg}$$ player running south at $$8.0\ \mathrm{m/s}. If $$they stick together after the collision, what is their final velocity?

Accepted Answer

$$v_f = -1.6\ \mathrm{m/s}$$

Question 12

Which of the following best explains why momentum is a vector quantity?

Accepted Answer

It depends on both mass and velocity, which have magnitude and direction.

Question 13

A $$0.5\ \mathrm{kg}$$ ball moving at $$2.0\ \mathrm{m/s}$$ collides with a stationary $$0.5\ \mathrm{kg}$$ ball in a perfectly elastic collision. What is the velocity of the first ball after the collision?

Accepted Answer

$$0\ \mathrm{m/s}$$

Question 14

Which formula is used to calculate the center of mass for discrete particles along the $$x-$$axis?

Accepted Answer

$$x_{CM} = \frac{\sum m_i x_i}{\sum m_i}$$

Question 15

A $$2.0\ \mathrm{kg}$$ cart moving at $$3.0\ \mathrm{m/s}$$ collides and sticks to a $$1.0\ \mathrm{kg}$$ cart at rest. What is their final velocity?

Accepted Answer

$$v_f = 2.0\ \mathrm{m/s}$$

Question 16

Which of the following is a real-world example of an inelastic collision?

Accepted Answer

A car crash where the vehicles crumple and lose kinetic energy.

Question 17

If a force $$F$$ acts on an object for a time interval $$\Delta t$$, what is the impulse delivered to the object?

Accepted Answer

$$J = F \Delta t$$

Question 18

Which of the following is NOT conserved in a perfectly inelastic collision?

Accepted Answer

Kinetic energy

Question 19

A $$0.2\ \mathrm{kg}$$ ball moving at $$5.0\ \mathrm{m/s}$$ collides with a $$0.3\ \mathrm{kg}$$ ball at rest in an elastic collision. What is the velocity of the $$0.2\ \mathrm{kg}$$ ball after the collision?

Accepted Answer

$$v_{1f} = -1.0\ \mathrm{m/s}$$

Center of Mass and Momentum: Study Notes and Problem Set

Study Guide - Practice Questions

Study Guide - Flashcards