Normal bounce

Classical Mechanics Level 2

A ball of mass $m$ is dropped from some height in a (uniform) gravitational field of $g$ . It reaches the ground and bounces directly upward, to 70% of its original height. During the bounce, the ball is in contact with the ground for a small, non-zero time interval of $\delta t$ .

What can be said about the normal force between the ball and ground during the interval $\delta t?$

N = 0

on average

N > mg

on average

N = mg

during the entire bounce

N = mg

on average, but

N > mg

during part of the time

N < mg

on average