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Homework Help: Mechanical Energy

  1. Mar 28, 2015 #1
    1. The problem statement, all variables and given/known data
    You do 100 J of work while pulling a child back on a swing, whose chain is 2.0 m long, until the swing makes an angle of 30.0° with the vertical. a) What is the child's mass? (Consider the swing itself and the chain massless) b) Upon releasing the swing from this position, what will the speed of the child be at the bottom of the arc?

    2. Relevant equations
    mgh = 1/2 mv^2

    3. The attempt at a solution
    After doing some trig, I get the height difference of the swing to be 0.267m; we now have h in mgh.

    since he exerted 100 Js, we set mgh = 100, solving for m

    m = 38.21 kg

    now we want to find the speed at the bottom of the arc.

    we set mgh = 1/2 mv^2

    Mass cancels out

    we solve for V, which should be 2.287 m/s.

    Can someone verify if my answers are correct?
  2. jcsd
  3. Mar 28, 2015 #2


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    Homework Helper
    Gold Member
    2017 Award

    Your work looks good to me.
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