A boat is able to move through still water at 20 m/s. It makes a round trip to a

Question

A boat is able to move through still water at 20 m/s. It makes a round trip to a town 3 km upstream. If the river flows at 5 m/s, the time required for this trip is ______ .


If possible, it would be most beneficial if the answer came with a diagram with the component vectors and the resultant vector (if at least for one part of the trip). (Also, try not to explain the answer by saying the velocities are additive. Or if you do, then please say more than simply stating 20 -5 =15 m/s and 20 +5= 25 m/s.)

Thanks.

Explanation / Answer

Hi, Since in the first part of journey the boat is going in opposite direction to the river flow, resultant velocity of the boat during upstream = 20m/s - 5m/s = 15m/s
  Hence time taken to go up stream:
t1 = d/s  = 3000 / 15 = 200 s.

And during the remaining part of its journey, the boat is moving in the same direction as the water is moving. Hence resultant velocity of boat during down stream is    20m/s + 5m/s = 25m/s
Hence time takne to come back: t2 = d/s = 3000 / 25 = 120 s.

Hence the total time takne to travel round trip is 120 + 200 = 320 s.
Hope this helps you.

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