Q. Rain drops fall vertically at a speed of $20ms^{- 1}$. At what angle do they fall on the wind screen of a car moving with a velocity of $15ms^{- 1}$, if the wind screen velocity inclined at an angle of 23${^\circ}$ to the vertical? $\left( \cot^{- 1}{\left\lbrack \frac{4}{3} \right\rbrack \approx 36{^\circ}} \right)$
A) 60${^\circ}$
B) 30${^\circ}$
C) 45${^\circ}$
D) 90${^\circ}$
Explanation
(a) tan(90${^\circ} - \theta$)$= \frac{20}{15}$
$\therefore cot\theta = \frac{20}{15} = \frac{4}{3}$
$\Rightarrow \ \theta = 37{^\circ}$
$\therefore\ \theta = 37{^\circ} + 23{^\circ}$
$= 60{^\circ}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.