A kid slides down an icy (frictionless) hill starting from rest. At the top his gravitational potential energy is 500 J. He slides part way down the hill to a point where his gravitational potential energy is 200 J. His kinetic energy at that point will be

Question

Quizplus · Accepted Answer

The conservation of energy in the absence of friction tells us that the initial potential energy must be equal to the sum of the final potential energy and the kinetic energy at that point. So:
Initial potential energy = 500 J
Final potential energy = 200 J
Kinetic energy at that point = initial potential energy - final potential energy = 500 J - 200 J = 300 J. Therefore, the correct choice is B.

A Kid Slides Down an Icy (Frictionless) Hill Starting from Rest