Question
A man standing on a road holds his umbrella at 30∘ with the vertical to keep the rain away. He throws the umbrella and starts running at 10 km/hr. He finds that raindrops are hitting his head vertically, the speed of raindrops with respect to the road will be
Answer: Option B
:
B
When the man is at rest w.r.t the the ground, the rain comes to him at an angle 30∘ with the vertical. This is the direction of the velocity
of raindrops with respect to the ground.
Here ⃗vrg = velocity of rain with respect to the ground
⃗vmg = velocity of the main with respect to the ground
and ⃗vrm = velocity of the rain with respect to the man.
We have ⃗vrg =⃗vrm +⃗vmg ... (i)
⃗vrg sin 30∘= ⃗vmg = 10 km/hr
or ⃗vrg = 10sin30∘ = 20 km/hr
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:
B
When the man is at rest w.r.t the the ground, the rain comes to him at an angle 30∘ with the vertical. This is the direction of the velocity
of raindrops with respect to the ground.
Here ⃗vrg = velocity of rain with respect to the ground
⃗vmg = velocity of the main with respect to the ground
and ⃗vrm = velocity of the rain with respect to the man.
We have ⃗vrg =⃗vrm +⃗vmg ... (i)
⃗vrg sin 30∘= ⃗vmg = 10 km/hr
or ⃗vrg = 10sin30∘ = 20 km/hr
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