Question 1

Which of the following best describes the physical quantity 'momentum' for a moving object?

Accepted Answer

Momentum is a vector quantity equal to the product of mass and velocity.

Question 2

A 2 kg ball is moving east at 3 m/s. What is its momentum vector?

Accepted Answer

$$\vec{p} = 6\ \mathrm{kg\cdot m/s}$$, east

Question 3

Which of the following statements about the conservation of momentum is correct?

Accepted Answer

Momentum is conserved in a system if no external forces act on it.

Question 4

A car (mass $$1000\ \mathrm{kg}$$, velocity $$15\ \mathrm{m/s}$$ east) and a truck (mass $$2000\ \mathrm{kg}$$, velocity $$10\ \mathrm{m/s}$$ north) are moving. What is the magnitude of the total momentum of the system?

Accepted Answer

$$18,027\ \mathrm{kg\cdot m/s}$$

Question 5

Newton’s second law can be rewritten in terms of momentum as:

Accepted Answer

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

Question 6

If you throw a ball down onto the floor and it bounces back, is the momentum of the ball conserved in this process?

Accepted Answer

No, because the ball feels an external force from the floor.

Question 7

In the rifle recoil scenario, a $$5.00\ \mathrm{g}$$ bullet is fired at $$300\ \mathrm{m/s}$$ from a $$3.00\ \mathrm{kg}$$ rifle. What is the recoil velocity of the rifle?

Accepted Answer

$$-0.5\ \mathrm{m/s}$$

Question 8

An astronaut (mass $$100\ \mathrm{kg}) $$throws a $$1.0\ \mathrm{kg}$$ wrench at $$10.0\ \mathrm{m/s} in $$space. What is the astronaut's velocity after throwing the wrench?

Accepted Answer

$$-0.1\ \mathrm{m/s}$$

Question 9

Which of the following is the correct unit for impulse?

Accepted Answer

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

Question 10

How is impulse ($$\vec{J}) $$related to the change in momentum ($$\Delta \vec{p}$$)?

Accepted Answer

$$\vec{J} = \Delta \vec{p}$$

Question 11

A dish falls and lands on a soft carpet instead of a hard floor. What happens to the change in momentum?

Accepted Answer

The change in momentum is the same in both cases.

Question 12

Why is it safer to hit a haystack than a concrete wall if your car is out of control?

Accepted Answer

The haystack increases the time of contact, reducing the average force.

Question 13

Which of the following is true about momentum conservation in collisions?

Accepted Answer

Momentum is conserved in elastic, inelastic, and completely inelastic collisions if no external forces act.

Question 14

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

Accepted Answer

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

Question 15

Which of the following best describes an elastic collision?

Accepted Answer

Total kinetic energy is conserved.

Question 16

A $$0.2\ \mathrm{kg}$$ ball moving at $$5\ \mathrm{m/s}$$ collides elastically with a stationary $$0.2\ \mathrm{kg}$$ ball. What is the velocity of the first ball after the collision?

Accepted Answer

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

Question 17

During a collision, which of the following is always true if no external forces act?

Accepted Answer

Total momentum is always conserved.

Question 18

A golfer follows through with his swing, increasing the time of contact with the ball. What effect does this have?

Accepted Answer

It increases the impulse and the ball's momentum.

Question 19

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

Accepted Answer

$$J = F \cdot \Delta t$$

Chapter 8: Momentum, Impulse, and Collisions – Study Notes

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