Problem 1.173

A particle of mass $m$ having collided with a stationary particle of mass $M$ deviated by an angle $\pi / 2$ whereas the particle $M$ recoiled at an angle $\theta=30^{\circ}$ to the direction of the initial motion of the particle $m .$ How much (in per cent) and in what way has the kinetic energy of this system changed after the collision, if $M / m=$ $=5.0 ?$