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Calculate the time of a swimmer

  1. Aug 30, 2011 #1
    A child, who is 45 m from the bank of a river, is being carried helplessly downstream by the river's swift current of 1.0 m/s . As the child passes a lifeguard on the river's bank, the lifeguard starts swimming in a straight line until she reaches the child at a point downstream.

    a)If the lifeguard can swim at a speed of 2.0 m/s relative to the water, how long does it take her to reach the child?
    b)How far downstream does the lifeguard intercept the child?

    Please help me to get started on this problem.
    Which equation should I use?

    Thank you
  2. jcsd
  3. Aug 30, 2011 #2


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    Displacement equals velocity times time. Combine that with the Pythagorean theorem. :wink:

    (Hint: The displacements involved form a triangle)
  4. Aug 30, 2011 #3


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    (Another hint: This problem is a little bit tricky, because the given speed at which the lifeguard can swim is 2 m/s relative to the water. So before you figure out the final answer, you'll have to to take this into account.)
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