Question

if you drop a softball from just above your knee, the kinetic energy of the ball just before it hits the ground is about 1 jule, true or false? if false, explain why

Answer 1

False.

The mass of a softball is approximately 200 g (0.2 kg), while the knees are located approximately at 30 cm (0.3 m) from the ground. It means that the gravitational potential energy of the ball when it is dropped is
$U=mgh=(0.2 kg)(9.81 m/s^2)(0.3 m)=0.6 J$

This corresponds to the total mechanical energy of the ball at the moment it is dropped, because there is no kinetic energy (the ball starts from rest). Then the ball is dropped, and just before it hits the ground, all this energy is converted into kinetic energy: but energy cannot be created, so its final kinetic energy cannot be greater than 0.6 J.