Question

A ball is thrown vertically upwards at 19.6 m/s. For its complete trip (up and back down to the starting position), its average speed is:

Answer 1

When the ball reaches its original position, it will have the same speed (but would be traveling in the opposite direction). So the average speed is

$\dfrac{19.6\,\frac{\mathrm m}{\mathrm s}-19.6\,\frac{\mathrm m}{\mathrm s}}{\Delta t}=0$

regardless of how long the ball was in the air.