Collisions and momentum: practice

8 marksCore physics3.4.1.6

Trolley A, of mass 0.80 kg, moves at

1.5\,\mathrm{m\,s^{-1}}

along a level track towards trolley B, of mass 1.2 kg, which is at rest. The trolleys collide and stick together. Friction is negligible.

Part 1

Calculate the speed of the trolleys immediately after the collision.

[2 marks]

Part 2

Show that about 0.5 J of kinetic energy is transferred to other stores in the collision.

[2 marks]

Part 3

The collision lasts 0.050 s. Calculate the average force that A exerts on B during the collision.

[2 marks]

Part 4

Explain why the total momentum of the trolleys is conserved in this collision but their total kinetic energy is not.

[2 marks]

1 marksCore physics3.4.1.6

Two objects collide. No external resultant force acts on them.

Which quantity is always conserved in the collision?

[1 mark]

1 marksCore physics3.4.1.6

A rifle of mass 4.0 kg, initially at rest, fires a bullet of mass 0.010 kg at

400\,\mathrm{m\,s^{-1}}

.

What is the recoil speed of the rifle?

[1 mark]

5 marksCore physics3.4.1.6

On a smooth track, ball A of mass 0.20 kg moves at

3.0\,\mathrm{m\,s^{-1}}

towards ball B of mass 0.30 kg, which is at rest. After a head-on collision, A rebounds at

0.60\,\mathrm{m\,s^{-1}}

.

Part 1

Calculate the velocity of B after the collision.

[2 marks]

Part 2

Show that the collision is elastic.

[2 marks]

Part 3

Calculate the magnitude of the change in momentum of ball A.

[1 mark]

4 marksUnfamiliar context3.4.1.6

A tennis ball of mass 0.058 kg hits a wall at right angles at

25\,\mathrm{m\,s^{-1}}

and rebounds along the same line at

20\,\mathrm{m\,s^{-1}}

. It is in contact with the wall for 4.0 ms.

Part 1

Calculate the magnitude of the change in momentum of the ball.

[1 mark]

Part 2

Calculate the average force the wall exerts on the ball.

[1 mark]

Part 3

The ball's momentum is not conserved. Explain why this does not break the law of conservation of momentum.

[2 marks]

5 marksUnfamiliar context3.4.1.6

A stationary nucleus of mass 238 u emits an alpha particle of mass 4.0 u at a speed of

1.5 \times 10^{7}\,\mathrm{m\,s^{-1}}

. The remaining nucleus has mass 234 u. Relativistic effects can be ignored.

Part 1

Calculate the recoil speed of the remaining nucleus.

[2 marks]

Part 2

Calculate the ratio of the alpha particle's kinetic energy to the kinetic energy of the recoiling nucleus.

[2 marks]

Part 3

Explain why almost all of the kinetic energy released goes to the alpha particle.

[1 mark]

3 marksCore physics3.4.1.6

Two trolleys, of mass 1.5 kg and 0.50 kg, are held at rest on a level track with a compressed spring between them. When released, the 0.50 kg trolley moves off at

1.2\,\mathrm{m\,s^{-1}}

.

Part 1

Calculate the speed of the 1.5 kg trolley.

[1 mark]

Part 2

Calculate the energy that was stored in the spring, assuming it is all transferred to kinetic energy.

[2 marks]