To a man walking at the rate of 3km/h the rain appears to fall vertically. When he increases his speed to 6km/h, it appears to meet him at an angle of 45∘ with vertical. Find the speed of rain.
A
3km/h
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B
3√2km/h
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C
2√3km/h
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D
32km/h
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Solution
The correct option is B3√2km/h Le the velocity of rain w.r.t ground, →Vr=x^i+y^j
Let Case (i): When the man is walking at the rate of 3km/h. Relative velocity of rain w.r.t man, →Vrm=→Vr−→Vm=−(x^i+y^j)+3^i=(3−x)^i−y^j Since rain appears to fall vertically, x− component =0 ⇒x=3 Case (ii): When the man is walking at the rate of 6km/h →Vrm=(6−x)^i−y^j Now rain appears to fall at an angle of 45∘ to the vertical. ⇒tan45∘=VyVx=−y6−x=yx−6=y−3 (as x=3) ⇒y=−3 ⇒→Vr=3^i−3^j |→Vr|=√32+(−3)2=3√2km/h