A-motor-boat-going-downstream-overcomes-a-float-at-a-point-A-60-minutes-later-it-turns-and-after-some-time-passes-the-float-at-a-distance-of-12-km-from-the-point-A-Find-the-velocity-of-the-stream-a

Question Number 13570 by Tinkutara last updated on 21/May/17

A motor boat going downstream

overcomes a float at a point A . 60 minutes

later it turns and after some time passes

the float at a distance of 12 km from

the point A . Find the velocity of the stream

(assuming constant velocity for the

boat in still water)

Answered by ajfour last updated on 21/May/17

boat moves from A for t_{1} = 1 h

with velocity u + v . [u = stream velocity]

it turns back, moving with speed

v - u, for time = t_{2}, whereupon

it meets the float again .

the float has come down a

distance d = 12 km .

u (t_{1} + t_{2}) = d \dots . . (i)

(u + v) t_{1} - (v - u) t_{2} = d \dots . (ii)

from eq . (ii)

u (t_{1} + t_{2}) + v (t_{1} - t_{2}) = d

using (i) in (ii),

t_{2} = t_{1} = 1 h

so, u = \frac{d}{(t_{1} + t_{2})} = \frac{12 km}{2 h}

u = 6 km / h .

Commented by Tinkutara last updated on 21/May/17

Thanks Sir!