Question

A small box starts sliding from rest at the top of the frictionless track of radius $R$. The initial height of the box equal to $2R$ above a horizontal surface. At the moment, the box leaves the bottom of the track, a ball of the same mass as the box is dropped from the same height at the bottom of the track.
Find out which of the following quantities must decrease as the box slides down the track?

• A. The normal force on the box
• B. The net force on the box
• C. The kinetic energy of the box
• D. The potential energy of the box
• E. The total mechanical energy (kinetic + potential) of the box

Answer 1

Answer: (D)

The potential energy of the box

When box comes down its height $2R$ from the horizontal surface is decreasing therefore its potential energy $U=mg\times 2R$ decreases whereas kinetic energy increases.