A river of width 200 m is flowing from west | vedclass

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(C) Given: Width of the river $d = 200 \ m$, velocity of river $v_R = 18 \ km/h = 18 	imes \frac{5}{18} = 5 \ m/s$, velocity of boat in still water $

Vedclass · Accepted Answer

$40 \ s$ and $200 \ m$

Vedclass · Answer

(C) Given: Width of the river $d = 200 \ m$, velocity of river $v_R = 18 \ km/h = 18 	imes \frac{5}{18} = 5 \ m/s$, velocity of boat in still water $v_{BR} = 36 \ km/h = 36 	imes \frac{5}{18} = 10 \ m/s$.To cross the river in minimum time, the boat must head perpendicular to the river flow.The time taken to cross the river once is $t = \frac{d}{v_{BR}} = \frac{200}{10} = 20 \ s$.For a round trip (going and coming back), the total time taken is $T = 20 + 20 = 40 \ s$.During this time, the boat is carried downstream by the river flow. The velocity of the boat relative to the ground along the river bank is $v_R = 5 \ m/s$.The displacement along the river bank is $x = v_R 	imes T = 5 	imes 40 = 200 \ m$.

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