Question

A car is moving in a rainstorm at a speed of $36\text{km/hr}$. The rain drops fall vertically w.r.t the ground with a constant speed of $20\text{m/s}$. The speed of the raindrops w.r.t the car is

• A. $10\sqrt{5}\text{m/s}$
• B. $50\sqrt{5}\text{m/s}$
• C. $10\sqrt{2}0\text{m/s}$
• D. $5\sqrt{5}\text{m/s}$

Answer 1

The correct option is A $10\sqrt{5}\text{m/s}$


Velocity of car = $v_c=36\text{km/h}=10\text{m/s}$
Velocity of rain drops = $v_r=20\text{m/s}$
From the figure,
Speed of rain drops w.r.t car, $v_{cr}^2=v_c^2+v_r^2$
$v_{cr}=\sqrt{{10}^2+{20}^2}=10\sqrt{5}\text{m/s}$
Hence the correct option is (a).