Question

A curved surface is shown in figure. The portion BCD is frictionless. There are three spherical balls of identical radii and masses. Balls are released from rest one by one from A which is at a slightly greater height than C. With the surface AB, ball 1 has large enough friction to cause rolling down without slipping, ball 2 has a small friction and ball 3 has a negligible friction. For which balls is total mechanical energy conserved?

• A. 1 and 2
• B. 1 and 3
• C. 2 and 3
• D. Cannot be predicted

Answer 1

Answer: (B)

1 and 3

Answer 2

As ball 1 rolls down AB without slipping, friction is large enough to cause only rotational motion. However, no energy is lost due to friction. Ball 3 has negligible friction. Therefore, total mechanical energy is conserved in case of balls 1 and 3. Small friction in case of ball 2 involves some dissipation of energy.