Question

# A glass wind screen whose inclination with the vertical can be changed is mounted on a car. The car moves horizontally with a speed of ( 2 mathrm{m} / mathrm{s} ). At what angle ( alpha ) with the vertical should the wind screen be placed so that the rain drops falling vertically downwards with velocity ( 6 mathrm{m} / mathrm{s} ) strike the wind screen perpendicularly?

Solution

Velocity of rain with respect to car should be perpendicular to the screen.

relative velocity( =overrightarrow{v_{text {rain}}}-overrightarrow{v_{text {car}}} )

( tan alpha=frac{V_{r}}{V_{c}}=frac{6}{2}=3 )

( alpha=tan ^{-1} 3 )