The angles made by the windscreens of two motorcars with horizontal are $β_{1} = 30 º$ and $β_{2} = 15 º$ respectively. The first car is travelling with a velocity $v_{1}$ horizontally. The second car is travelling with a velocity $v_{2}$ in the same direction. The hail stones are falling vertically. Both the drivers observe that the hail stones rebound vertically after elastic collision with the windscreen. Find the ratio of $v_{1} / v_{2}$ .

Difficult

Solution