Q: A tennis player hits a 57 g ball with a force of 560 N for 0.0050 s. What is the speed of the ball as it leaves the racket, assuming it was initially at rest?

$$v = \frac{F \Delta t}{m} = \frac{560 \times 0.0050}{0.057} = 49.1 \text{ m/s}$$

Q: A 60 kg person lands straight down on the ground and comes to a halt in 0.10 s. What is the average force exerted by the ground on the person if their velocity just before contact is 6.0 m/s downward?

$$F = \frac{\Delta p}{\Delta t} = \frac{60 \times 6.0}{0.10} = 3600 \text{ N}$$

Question 1

A 50.0 kg person pushes off a 5.0 kg skateboard and moves to the left at 0.600 m/s. What is the speed and direction of the skateboard immediately after the push, assuming no external forces act on the system?

Accepted Answer

The skateboard moves to the right at 6.00 m/s.

Question 2

Which of the following best describes the law of conservation of linear momentum?

Accepted Answer

The total momentum of a system remains constant if no external force acts on the system.

Question 3

Two ice hockey players collide and stick together after the collision. Which type of collision is this?

Accepted Answer

Completely inelastic collision

Question 4

A $$1.50 x 10^3 kg $$car moving north at 35.0 m/s collides head-on with a $$7.50 x 10^3 kg $$truck moving south at 25.0 m/s. If they stick together after the collision, what is their velocity and direction immediately after?

Accepted Answer

They move south at 10.0 m/s.

Question 5

Which equation correctly expresses the linear momentum $$p of an $$object with mass $$m$$ and velocity $$v$$?

Accepted Answer

$$p = m v$$

Question 6

In a one-dimensional elastic collision between two objects, which quantities are conserved?

Accepted Answer

Both momentum and kinetic energy

Question 7

A tennis player hits a 57 g ball with a force of 560 N for 0.0050 s. What is the speed of the ball as it leaves the racket, assuming it was initially at rest?

Accepted Answer

$$v = \frac{F \Delta t}{m} = \frac{560 	imes 0.0050}{0.057} = 49.1 	ext{ m/s}$$

Question 8

Which of the following is true about the direction of the momentum vector?

Accepted Answer

It is always in the same direction as the velocity vector.

Question 9

A 60 kg person lands straight down on the ground and comes to a halt in 0.10 s. What is the average force exerted by the ground on the person if their velocity just before contact is 6.0 m/s downward?

Accepted Answer

$$F = \frac{\Delta p}{\Delta t} = \frac{60 	imes 6.0}{0.10} = 3600 	ext{ N}$$

Question 10

In a two-body collision, which statement is correct regarding the change in momentum of each object?

Accepted Answer

Both objects experience equal and opposite changes in momentum.

Question 11

A 1.60 kg block moving right at 4.00 m/s collides elastically with a 2.10 kg block moving left at 2.51 m/s. What is the velocity of the 1.60 kg block after the collision?

Accepted Answer

$$v_1$$' = \frac{($$m_1$$ - $$m_2$$)$$v_1 + 2m_2$$ $$v_2$$}{$$m_1$$ + $$m_2$$}$$

Question 12

Which of the following best explains why bending your knees when landing from a jump reduces the force of impact?

Accepted Answer

It increases the time interval over which the momentum changes, reducing the average force.

Question 13

A rock of mass $$m$$ falls freely under gravity. What is its momentum after time $$t if $$released from rest?

Accepted Answer

$$p = m g t$$

Question 14

During a collision, the product of the force and the duration of contact is known as:

Accepted Answer

Impulse

Question 15

Which of the following is true for a completely inelastic collision?

Accepted Answer

The colliding objects stick together after the collision.

Question 16

A boxer punches a 75 kg heavy bag at 8 m/s and stops it in 0.02 s. What is the average force exerted on the bag?

Accepted Answer

$$F = \frac{75 	imes 8}{0.02} = 30,000 	ext{ N}$$

Question 17

Which of the following is a vector quantity?

Accepted Answer

Linear momentum

Question 18

In a two-dimensional collision, how is the law of conservation of momentum applied?

Accepted Answer

Momentum is conserved independently in both the x and y directions.

Question 19

Which of the following is true about elastic collisions?

Accepted Answer

No mechanical energy is lost; both momentum and kinetic energy are conserved.

Chapter 8: Linear Momentum and Collisions – Study Notes

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