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The speed of a boat is 1.5 m/s in still water. One needs to cross a river of width 500 m with this boat. Along the direction of the river a strong wind is blowing with a speed of 0.9 m/s. The boat is oared to the opposite shore of the river, but the water current tries to send it in the direction of the river. Find the speed of the boat relative to the shore, then find the distance between the point where it starts to the point where it reaches the opposite shore, and then find the time it takes to cross the river.

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    $\begingroup$ Please note that Physics.StackExchange is not a homework help site. Please see this Meta post on asking homework questions and this Meta post for "check my work" problems $\endgroup$
    – ritvik1512
    Commented Feb 2, 2015 at 15:55

1 Answer 1

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  1. Think of the velocity of the boat as a vector. $1.5$ m/s in the x-direction (to the shore), $0.9$ m/s in the y-direction (in the direction of the river)
  2. As such, you can find the magnitude of the velocity vector, which we routinely call the speed of the boat
  3. The 500 meters in the x-direction will be covered in $500/1.5$ seconds.
  4. Using this time interval, multiply by $0.9$ m/s to get the distance covered in the y-direction.
  5. Now using Pythagoras' theorem, you can find the distance between point A and point B.

Lesson you should take away from this: vectors can be really useful concepts.

N.B. I don't think you're supposed to put your homework questions here, but seeing how you asked a similar question before (from your profile), I figured I'd help you out anyway.

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    $\begingroup$ don't feed the bears $\endgroup$
    – Jim
    Commented Feb 2, 2015 at 16:59

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