A curved suface is shown in figure. The portion BCD is free of friction. 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.
Wioth 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.
(a) For which ball is total mechanical energy conserved?
(b) Which ball(s) can reach D?
(c )For ball which do not reach D, which of the balls can reach back A?

Explanation

(a) As ball 1 is rolling down without slipping there is no dissipation of energy, hence total mechanical energy is conserved.
(b) Ball 1 acquires rotational energy, ball 2 loses energt by friction. They cannot cross at C. Ball # can cross over.
(c ) Balls 1 and 2 turn back before reaching C. Because of loss of energy, ball 2 cannot reach back to A. Ball 1 has a rotational motion in wrong sense when it reaches B. It cannot roll back to A because of kinetic friction.