Linear Momentum & Conservation (AQA A Level Physics)

A tennis ball of mass 60 g is struck by a tennis racket. The velocity of the ball changes as shown

What is the magnitude of the change in momentum of the ball?

Two spheres approach each other along the same straight line. Their speeds are u₁ and u₂ before collision, and v₁ and v₂ after collision, in the directions shown below

Which equation is correct if the collision is perfectly elastic?

A lorry of mass 18 tonnes is travelling at 25.0 m s^–1.

A car of mass 800 kg is travelling at 40.0 m s^–1 towards the lorry.

What is the magnitude of the total momentum?

• 1 tonne = 1000 kg

The diagram shows the masses and velocities of two trolleys about to collide

After the impact they move off together.

What is the total kinetic energy of the trolleys after the collision?

The diagram shows a cannon ball fired from a cannon

The mass of the cannon is 1600 kg and the mass of the cannon ball is 20 kg.

The recoil velocity of the cannon is 5 m s^–1 horizontally.

What is the horizontal velocity of the cannon ball?

A ball of mass 2 kg travelling at m s^–1 strikes a ball of mass 3 kg travelling at m s^–1. Both balls are moving along the same straight line as shown

After collision, both balls move at the same velocity v.

What is the magnitude of the velocity v?

A molecule of mass m travelling at speed v hits a wall in a direction perpendicular to the wall. The collision is elastic.

What are the changes in the momentum and in the kinetic energy of the molecule caused by the collision?

	change in momentum	change in kinetic energy
A	0	0
B	mv	mv2
C	mv2	0
D	−2mv	0

A moving object strikes a stationary object. The collision is inelastic. The objects move off together.

Which row shows the possible values of total momentum and total kinetic energy for the system before and after the collision?

	total momentum before collision / kg m s–1	total momentum after collision / kg m s–1	total kinetic energy before collision / J	total kinetic energy after collision / J
A	6	6	90	30
B	6	6	30	90
C	6	2	90	30
D	6	6	90	90

A resultant force of 5 N acts on a body for a time of 4.0 s.

Which graph could show the variation with time t of the momentum p of the body?

Two train carriages each of mass 7500 kg roll toward one another on a level track. One is travelling at 3.00 m s^–1 and the other at 1.50 m s^–1, as shown.

They collide and join together.

What is the kinetic energy lost during the collision?

Two trolley, A and B, are connected by an elastic chord, of negligible mass, as shown below. Trolley A is three times the mass of trolley B.

The two trolleys are pulled apart so that the elastic chord is stretched. The trolleys are then released at the same time and move towards each other.  The trolleys stick together on impact. 

Just before the trolleys collide, the speed of trolley A is 10 cm s^–1.

What is the speed of the trolleys after they collide?

A pellet gun fires 2 g pellets at a rate of 200 pellets per minute.  The pellets leave the pellet gun at a velocity of 20 m s^–1 and strike a fixed steel block.  The pellets rebound off the block with the same velocity as they were fired.

What is the average force exerted on the steel container over one minute?

The diagram below shows a block of mass 1.2 kg sliding down a rough slope from rest against a constant friction force of 1.5 N.

What is the momentum of the block along the slope after 4 seconds?

The variation of the force, F, with time, t, acting on a mass of 250 g is shown on the graph below.

The velocity of the body at t = 10 ms is 8 m s^–1.

What is the velocity of the body at t = 35 ms?

Particle A has a mass m and is moving towards a stationary particle, B, of mass M.  A is travelling with a velocity of u before colliding head on with particle B.  The collision between the particles is elastic.

What is the velocity of particle B after the collision? 

An object of mass 40 g travelling at 4.0 m s^–1 collides head on with a mass of 20 g travelling in the opposite direction at 3.5 m s^–1.  The collision between the masses is inelastic.

How much kinetic energy is lost after the collision?