Sample 1Medium
A diagram shows rain falling vertically downward at 4 m/s and a man walking horizontally due east at 3 m/s on level ground, holding an umbrella. In which direction should he tilt the umbrella to keep the rain off?
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The answer is D.
Velocity of rain relative to the man = v_rain − v_man: 4 m/s down plus 3 m/s towards the west. It makes tan⁻¹(3/4) with the vertical and comes at him from the east, so he tilts the umbrella forward, towards the east, at that angle.
- A.
Upright works only when the man stands still; relative to him the rain has a horizontal component.
- B.
The rain comes at him from the front (east), so tilting backward (west) leaves him exposed.
- C.
tan⁻¹(4/3) is the angle with the horizontal, not with the vertical.
NCERT: Class 11 Physics, Chapter 3