A ball is thrown straight up from the edge of a cliff of height H above the ground and later falls back past the same point before finally striking the ground at the foot of the cliff.
(a) Using a labelled time diagram, explain why the magnitude of the velocity of the ball when it passes the cliff edge on its way down is equal to its initial speed of projection.
(b) Briefly describe how this symmetry in motion changes, if at all, when air resistance cannot be neglected.
a. (a) Explanation using a time diagram of equal magnitudes of upward and downward velocities at the cliff edge
b. (b) Effect of air resistance on this symmetry