Question

Okay. How do I go about answering this question? And what is it really asking?

A watermelon has a mass of 118 kg. It is on a platform 5 m above the ground. When taken off the platform, it is allowed to slide down a ramp. How high above the ground is the watermelon at the moment its kinetic energy 4.61 kJ?

Answer 1

The initial potential energy of the watermelon is mass*acceleration*height or mgh for Earth. For practical purposes assume that total energy of the watermelon is constant. So the potential energy + the kinetic energy is constant. The kinetic energy is given at the point of interest. So the remaining potential energy is:
(118kg * g * 5m) - 4.61kj = ?
After you solve for the remaining potential energy, just use mgh again:
mgh = remaining potential energy
solve for h

Answer 2

Also, it is assumed there is no friction with the ramp.