7. Whilst looking over the edge of a vertical cliff, 122.5 metres in height, Jim dislodges a stone. The stone falls freely from rest towards the sea below.
Ignoring the effect of air resistance,
- calculate the time it would take for the stone to reach the sea,
- find the speed with which the stone would hit the water.
Two seconds after the stone begins to fall, Jim throws a tennis ball downwards at the stone. The tennis ball's initial speed is \(u \mathrm {~ms} ^ { - 1 }\) and it hits the stone before they both reach the water.
- Find the minimum value of \(u\).
- If you had taken air resistance into account in your calculations, what effect would this have had on your answer to part (c)? Explain your answer.
(2 marks)