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Homework Help: Mechanical energy problems

  1. Apr 20, 2017 #1
    1. The problem statement, all variables and given/known data
    A rock with a mass of 0.2 kg is dropped from a height of 20 m. At what velocity does the rock strike the ground?


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

    3. The attempt at a solution
    0.2x9.81x20=1/2mv^2.
    39.24=.1(v^2)
    392.4=v^2
    v=19.8 m/s
    First time doing one of these problems, does my answer seem reasonable and did I use the right set of equations for this particular problem and did i set it up right? Thanks
     
  2. jcsd
  3. Apr 20, 2017 #2

    gneill

    User Avatar

    Staff: Mentor

    Looks good. Well done.

    Note that if you'd done the math symbolically first (before plugging in any numbers) you could have saved some arithmetic:

    1/2mv^2 = mgh

    Note that the "m" cancels on either side.
     
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