A kid slides down an icy (frictionless) hill starting from rest. At the top his gravitational potential energy is 500 J.
-Suppose after reaching the bottom he then continues sliding up another icy slope on the other side of the valley.When he finally comes to a stop he will have reached a height
A)equal to the height he started from on the other hill.
B)less than the height he started from on the other hill.
C)more than the height he started from on the other hill.
D)none of the above

Question

Quizplus · Accepted Answer

The conservation of energy principle tells us that the kid's total energy (potential + kinetic) at the top of the first hill is equal to his total energy at any point on the second hill. Since the second hill is also icy and frictionless, we can assume that there is no energy lost due to friction. Therefore, the kid will continue sliding up the second hill with the same amount of total energy as he had at the bottom of the first hill.

It follows that the kid will reach a height on the second hill that is equal to the height he started from on the first hill, since his initial potential energy on the first hill was converted entirely to kinetic energy at the bottom, and then entirely back to potential energy at the top of the second hill. Therefore, the answer is A.

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