JEE Advanced Model Paper 16 with solutions for online practice

Five identical balls each of mass m and radius r are strung like beads at random and atrest along a smooth, rigid horizontal thin rod of length L, mounted betweenimmovable supports. Assume 10r < L and that the collision between balls or betweenballs and supports are elastic. If one ball is struck horizontally so as to acquire a speedv, the average force felt by the support is