Hail storms are observed to strike the surface of frozen lake at $30^{\circ }$ with the vertical and rebound at $60^{\circ}$ with vertical, Assume contact to be smooth, the coefficient of restitution,

Question

$$(a)\;e=\frac{1}{\sqrt 3} \quad (b)\;e=\frac{1}{3} \quad (c)\;e=\sqrt 3 \quad (d)\;e=3$$