Question

a man can row a boat at 10 kmph in still water and the speed of the stream is 5kmph. what is the time taken to row a distance of 90 km down the stream ?

Answer 1

Hope this helps.

Upstream speed=Speed in still water-Speed of stream.

Downstream speed-Speed in still water+Speed of stream.

The trick lies in identifying the various speeds and mindfully using it.

Answer 2

Given :

Speed of boat , v = 10 kmph .

Speed of stream , u = 5 kmph .

To Find :

The time taken to row a distance of 90 km down the stream .

Solution :

We know , downstream velocity is given by v + u .

Now , time is given by :

$t=\dfrac{D}{v+u}\\\\t=\dfrac{90}{10+5 }\\\\t= 6\ hours$

Therefore , time taken to row a distance of 90 km down the stream is 6 hours .

Learn More :

Relative velocity

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