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)


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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

	$boat moves from A for t_{1} = 1 h$ $with velocity u + v . [u = stream velocity]$ $it turns back, moving with speed$ $v - u, for time = t_{2}, whereupon$ $it meets the float again .$ $the float has come down a$ $distance d = 12 km .$ $u (t_{1} + t_{2}) = d . . . . . (i)$ $(u + v) t_{1} - (v - u) t_{2} = d . . . . (ii)$ $from eq . (ii)$ $u (t_{1} + t_{2}) + v (t_{1} - t_{2}) = d$ $using (i) in (ii),$ $t_{2} = t_{1} = 1 h$ $so, u = \frac{d}{(t_{1} + t_{2})} = \frac{12 km}{2 h}$ $u = 6 km / h .$
	Commented by Tinkutara last updated on 21/May/17

	$Thanks Sir!$
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