Question

Rain drops fall vertically at a speed of $20 \,ms ^{-1}$. At what angle do they fall on the wind screen of a car moving with a velocity of $15\, ms ^{-1}$, if the wind screen velocity inclined at an angle of $23^{\circ}$ to the vertical?
$\left[\cot ^{-1}\left(\frac{4}{3}\right) \approx 36^{\circ}\right]$

• A. $60^{\circ}$
• B. $30^{\circ}$
• C. $45^{\circ}$
• D. $90^{\circ}$

Answer 1

Answer: (A)

Let the required angle is $\theta$.
$ \tan \left(90^{\circ}-\theta\right)=\frac{20}{15} $
$\therefore \cos \theta=\frac{20}{15}=\frac{4}{3} $
$ \Rightarrow \theta=37^{\circ} $
$ \therefore \theta=37^{\circ}+23^{\circ}=60^{\circ}$