7 A particle \(P\) of mass 0.2 kg is projected vertically upwards from horizontal ground with speed \(25 \mathrm {~ms} ^ { - 1 }\).
- Show that the speed of \(P\) when it reaches 20 m above the ground is \(15 \mathrm {~ms} ^ { - 1 }\).
When \(P\) reaches 20 m above the ground it collides with a second particle \(Q\) of mass 0.1 kg which is moving downwards at \(20 \mathrm {~ms} ^ { - 1 } . P\) is brought to instantaneous rest in the collision. - Find the velocity of \(Q\) immediately after the collision.
When \(P\) reaches the ground it rebounds back directly upwards with half of the speed that it had immediately before hitting the ground. - Find the height above the ground at which \(P\) and \(Q\) next collide.
If you use the following page to complete the answer to any question, the question number must be clearly shown.