Question 1

A 2 kg cart moving at $$3\ \mathrm{m/s}$$ collides head-on and sticks to a stationary 1 kg cart on a frictionless track. What is the final velocity of the combined carts after the collision?

Accepted Answer

$$2\ \mathrm{m/s}$$

Question 2

Which of the following statements about momentum is TRUE?

Accepted Answer

Momentum is a vector quantity and is always conserved in isolated systems.

Question 3

A gun of mass $$3\ \mathrm{kg}$$ fires a $$0.01\ \mathrm{kg}$$ bullet at $$500\ \mathrm{m/s}. $$What is the recoil velocity of the gun?

Accepted Answer

$$-1.7\ \mathrm{m/s}$$

Question 4

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

Accepted Answer

Momentum is conserved, but kinetic energy is not.

Question 5

A $$0.3\ \mathrm{kg}$$ baseball is hit by a bat, changing its velocity from $$-42\ \mathrm{m/s} to$$ $$+80\ \mathrm{m/s} in$$ $$0.01\ \mathrm{s}. $$What is the magnitude of the average force exerted by the bat?

Accepted Answer

$$3700\ \mathrm{N}$$

Question 6

Which equation correctly relates impulse $$J to $$the change in momentum $$\Delta p$$?

Accepted Answer

$$J = F_{\mathrm{net}} \cdot \Delta t = \Delta p$$

Question 7

A $$10\ \mathrm{kg}$$ mass moving at $$2\ \mathrm{m/s}$$ collides elastically with a $$1\ \mathrm{kg}$$ mass at rest. What is the final velocity of the $$1\ \mathrm{kg}$$ mass after the collision?

Accepted Answer

$$3.64\ \mathrm{m/s}$$

Question 8

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 translational motion.

Question 9

A $$0.02\ \mathrm{kg}$$ bullet is fired into a $$2\ \mathrm{kg}$$ block hanging from a string. The bullet embeds in the block, and together they rise to a height $$h. $$Which conservation laws must be used to determine the bullet's initial speed?

Accepted Answer

Conservation of momentum during the collision and conservation of energy during the swing.

Question 10

In a 1D elastic collision between two objects, which of the following is true about their relative velocities?

Accepted Answer

The relative velocity after the collision is the negative of the relative velocity before the collision.

Question 11

A $$4-$$mass system forms a square of edge length $$d. $$The masses are $$m$$, $$m$$, $$m$$, and $$3m. $$Where is the center of mass located along the $$x-$$axis?

Accepted Answer

$$0.67d$$

Question 12

A rocket moves in space by expelling fuel out the back. Which principle explains why this works?

Accepted Answer

Conservation of momentum

Question 13

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

Accepted Answer

The system must be at rest initially.

Question 14

A $$2\ \mathrm{kg}$$ object moving at $$5\ \mathrm{m/s}$$ collides with a $$3\ \mathrm{kg}$$ object moving at $$-2\ \mathrm{m/s} ($$opposite direction). What is the total momentum before the collision?

Accepted Answer

$$1\ \mathrm{kg\cdot m/s}$$

Question 15

Which of the following best describes an impulse in physics?

Accepted Answer

A large force acting over a short period of time, causing a change in momentum.

Question 16

If the net external force on a system is zero, what can be said about the motion of the center of mass?

Accepted Answer

It moves with constant velocity.

Question 17

A $$1\ \mathrm{kg}$$ ball moving at $$4\ \mathrm{m/s}$$ collides elastically with a $$2\ \mathrm{kg}$$ ball at rest. What is the velocity of the $$1\ \mathrm{kg}$$ ball after the collision?

Accepted Answer

$$1.33\ \mathrm{m/s}$$

Question 18

Which of the following is the correct formula for the center of mass $$R of a $$system of particles?

Accepted Answer

$$R = \frac{\sum m_i r_i}{M}$$

Question 19

A bomb explodes in mid-air into several fragments. What can be said about the motion of the center of mass of the fragments?

Accepted Answer

It continues to move as if the bomb had not exploded.

Linear Momentum and Collisions: Conservation Principles, Impulse, and Center of Mass

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