$*15-72.$ The man A has a weight of $100$ lb and jumps from rest onto the platform $P$ that has a weight of $60$ lb $.$ The platform is mounted on a spring, which has a stiffness $k=200l\frac{b}{f}t.$ If the coefficient of restitution between the man and the platform is $e=0\mathrm{.}6,$ and the man holds himself rigid during the motion, determine the required height $h$ of the jump if the maximum compression of the spring becomes $2$ ft $.$

$15-47.$ The $30-Mg$ freight car A and $15-Mg$ freight car $B$ are moving towards each other with the velocities shown. Determine the maximum compression of the spring mounted on car $A.$ Neglect rolling resistance.

Prob. $15-47$