(a)[2]
Determine the speed of $A$ after it has risen to a height of $20\,\text{m}$ above the ground.
(b)[2]
At the point when $A$ is at a height of $20\,\text{m}$, it strikes a particle $B$ of mass $0.3\,\text{kg}$, which is travelling downwards along the same vertical line as $A$ at $32.5\,\text{m s}^{-1}$. During the collision between the two particles, $B$ is stopped instantaneously. Demonstrate that the velocity of $A$ immediately after the collision is $4.5\,\text{m s}^{-1}$ downwards.
(c)[4]
Determine the time interval between $A$ and $B$ arriving at the ground. Assume that $A$ does not rebound when it reaches the ground.