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+1 vote
43.9k views
in Physics by (45.1k points)
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A girl standing on road holds her umbrella at 45º with the vertical to keep the rain away. If she starts running without umbrella with a speed of 15√2 kmh -1 , the rain drops hit her head vertically. The speed of rain drops with respect to the moving girl is :

(A) 30 Kmh -1

(B) 25/√2 Kmh -1

(C) 30/√2 Kmh -1

(D) 25 Kmh-1

2 Answers

+1 vote
by (15.0k points)
selected by
 
Best answer

Correct option is (c) \( \frac{30} {\sqrt 2}\)  kmh-1

\(\vec{v_{rg}} = \vec {v_r} - \vec {v_g}\)

From the above diagram, velocity of the raindrop wrt ground will be,

\(|\vec{v_r}| = \sqrt{(15\sqrt 2)^2 + (15\sqrt 2)^2}\)

\(= 30 \) kmh-1

And velocity of the raindrop wrt the moving girl will be,

\(|\vec {v_{rg}}| = 15\sqrt 2\)

\(= \frac{30} {\sqrt 2}\) kmh-1

+2 votes
by (44.0k points)

Correct option is (C) 30/√2 Kmh -1

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