Math

a man can swim with a speed of 4 km per hr in still water. How long does he take to cross a river 1 km wide if the river flows steadily at 3 km per hr and he makes his strokes normal to the river current? How far down the river does he go when he reaches the other bank?

Ans: the speed of the swimmer will be approx 1 km

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  1. Are you studying vectors?

    the resulting velocity vector is (4,0) + (0,3)
    = (4,3)
    magnitude of vector = √(4^2+3^2)
    = √25 = 5

    time to go 1 km at 5 km/h
    = 1/5 hours or 12 minutes

    angle between the resultant an normal:
    tanØ = 3/4
    Ø = 36.87°

    for distance down the river where he lands:
    tanØ = x/1
    x = tanØ = .75

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    posted by Reiny

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