In the spring mass system shown in the figure, the spring is compressed by $x_0=\frac{mg}{3k}$ from its natural length and the block is released from rest. The speed of the block, when it passes through the point $P$ at means position, is

Five identical balls each of mass $m$ are placed adjacent to each other at rest on a smooth horizontal floor. An another identical ball moving with speed $v$ collides elastically with the left most ball as shown in figure. After collision(s)

A bob of mass $\mathrm{m}$ is pulled along a circular arc by means of a constant horizontal force $P$ as shown. Work done by the force $P$ while lifting the bob from $A$ to $B$ is