Final answer:
A bouncing ball has zero gravitational potential energy at the point of contact with the ground. This corresponds to the instant when the ball's height is zero relative to the defined zero level (the ground), where all its mechanical energy is in the form of kinetic energy. The ball achieves maximum potential energy at the highest point in its trajectory.
Step-by-step explanation:
A bouncing ball will have zero gravitational potential energy when it is at the point of contact with the ground or the surface from which it bounces. This is because gravitational potential energy depends on the height of the object above a defined zero level, commonly chosen to be ground level for convenience. Therefore, as a ball bounces and momentarily comes into contact with the ground, its height above the ground is zero, and thus its gravitational potential energy is also zero at that instant. In a drawing, this is typically shown as a ball in direct contact with the horizontal surface it is bouncing from, with the label 'zero gravitational potential energy' at that point.
Using the Principle of Conservation of Mechanical Energy, we can understand that as a ball falls towards the ground, it transforms its potential energy into kinetic energy. At the moment of impact with the ground, where we've defined the gravitational potential energy to be zero, all the ball's energy is kinetic (if we ignore energy loss due to factors like air resistance or deformation of the ball). Then, as the ball rises, it converts its kinetic energy back into gravitational potential energy until its velocity is zero at the peak of its bounce, where its potential energy is at maximum.
The concept that objects have maximum potential energy at a maximum height is crucial because it allows us to solve problems involving gravitational potential energy by setting the zero level at the ground and measuring the height of the object above this zero level to calculate its potential energy.