Question

Which situation describes a system with decreasing gravitational potential energy?

Answer 1

An example of a system with decreasing gravitational potential energy is a ball in free fall. 

At its initial height h, the ball has a gravitational potential energy equal to
$U=mgh$
where m is the ball mass and g is the gravitational acceleration. As the ball falls toward the ground, its height h decreases, and so its gravitational potential energy decreases as well, according to the formula 
$U=mgh'$
where h' is the new height of the ball.