Suppose three identical steel balls Q; R; and S are placed on an undulating ground as illustrated in the diagram above. Which of the balls is/are in neutral equilibrium?

A. S only
B. Q only
C. R only
D. Q and S only

Correct Answer:

Option A = S only

Explanation

A system is in neutral equilibrium if its equilibrium is independent of displacements from its original position. A marble S on a flat horizontal surface is an example.