A steel ball of mass 0.500 $\mathrm{kg}$ is fastened to a cord that is 70.0 $\mathrm{cm}$ long
and fixed at the far end. The ball is then
released when the cord is horizontal (Fig. $9-65$ ). At the bottom of its path,
the ball strikes a 2.50 $\mathrm{kg}$ steel block initially at rest on a frictionless surface.
The collision is elastic. Find (a) the speed of the ball and (b) the speed of
the block, both just after the collision.