5 Momentum 2021- 2020 IG

What is the relationship between the impulse acting on an object and the change in momentum of the object?

• impulse = change in momentum

• impulse = change in momentum × time

• impulse = change in momentum / time

• impulse = change in momentum / mass

A rocket is launched upwards from the surface of the Moon. Hot gases are ejected downwards over a very short period of time.

Which statement is not correct?

• The rocket experiences a downward force.

• The rocket experiences an upward force.

• The total momentum of the hot gases is equal to the momentum of the rocket.

• The total momentum of the hot gases and rocket when the hot gases have been ejected is zero.

A cricket ball has a mass of 0.16 kg. The ball travels at 30 m/s. The ball is hit by a bat with a force of 10 800 N.

After being hit, the ball moves off at 30 m/s in the opposite direction.

For how long was the ball in contact with the bat?

• 0.0004 s

• 0.00089 s

• 0.0044 s

• 0.015 s

A ball has a mass of 2.0 kg. The ball approaches a wall at a speed of 3.0 m/s and rebounds at a speed of 1.0 m/s.

What is the impulse on the wall?

• 4.0 N

• 4.0 N s

• 8.0 N

• 8.0 N s

A tennis ball has a mass of 57 g.

A tennis player hits the tennis ball with a tennis racket. The tennis ball has a velocity of 25 m/s when it hits the racket.

The velocity of the tennis ball when it leaves the player’s racket is 15 m/s in the opposite direction from its approaching direction. The average force exerted by the tennis racket on the ball is 35 N.

For how long is the tennis ball in contact with the tennis racket?

• 0.015 s

• 0.016 s

• 0.065 s

• 0.65 s

Object X moves to the right along a frictionless surface towards a stationary object Y, as shown.

They make a noise as they collide and then both objects move to the right.

Which equation is correct?

• change in momentum of X = change in momentum of Y

• impulse of force acting on X = impulse of force acting on Y

• kinetic energy of X before collision = (kinetic energy of X + kinetic energy of Y) after collision

• momentum of X before collision = (momentum of X + momentum of Y) after collision

A gas molecule strikes the wall of a container. The molecule rebounds with the same speed. What happens to the kinetic energy and what happens to the momentum of the molecule?

• kinetic energy: changes, momentum: changes

• kinetic energy: changes, momentum: stays the same

• kinetic energy: stays the same, momentum: changes

• kinetic energy: stays the same, momentum: stays the same

An object with a mass of 0.20 kg moves at 0.20 m/s, as shown. Which other object has a momentum that is identical to the momentum of this object?

• 0.20 kg at 0.20 m/s (downwards)

• 0.40 kg at 0.10 m/s (downwards)

• 0.40 kg at 0.10 m/s (rightwards)

• 0.20 kg at 0.20 m/s (leftwards)

A footballer kicks a stationary football. His foot is in contact with the ball for 0.050 s.

The mass of the ball is 0.40 kg. The speed of projection of the ball is 25 m/s.

What is the average force exerted on the ball by his foot?

• 0.32 N

• 0.50 N

• 200 N

• 1300 N

A ball of mass m falls vertically and hits a hard surface.

Its speed on hitting the surface is v₁. It rebounds vertically upwards with speed v₂.

What is the change in momentum of the ball?

• mv₁

• mv₂

• m(v₁ + v₂)

• m(v₂ − v₁)