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  • A motorboat going downstream overcame a raft at a point A;t = 60 min later it turned back and after some time passed the raft at a distance l = 6.0 km from the point A. Find the flow velocity. Assuming duty of motorboat is constant.

A motorboat going downstream overcame a raft at a point A;t = 60 min later it turned back and after some time passed the raft at a distance l = 6.0 km from the point A. Find the flow velocity. Assuming duty of motorboat is constant.

Answers (1)

Let the speed of still water be y and that of the boat be x.

During the downstream journey let the boat covers a distanced d. The distance d is covered in 60 minutes=1 hours. Therefore

(x+y)\times1=d.......(1)

Let during the upward journey the boat meet the raft at time t. Then the distance covered by boat in the upward journey is

(x-y)\times t=d-6.......(2)

During total time (1+t) raft travels a distance of 6 Km

Therefore

y(1+t)=6.......(3)

\\(1)-(3)\Rightarrow \\x-yt=d-6.......(4)\\

Equating LHS of (2) and (4)

\\xt-yt=x-yt\\t=1 hour

Therefore from (3)

y=3\ Km/h​​​​​​​

Posted by

Safeer PP

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