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Homework Help: Calculating Work done by the Earth and the work done by the Spring

  1. Apr 24, 2010 #1
    1. The problem statement, all variables and given/known data
    A mass of 0.091 kg hangs from a vertical spring in the lab room. You pull down on the mass and throw it vertically downward. The speed of the mass just after leaving your hand is 3.80 m/s.
    2. Relevant equations
    (a) While the mass moves downward a distance of 0.09 m, how much work was done on the mass by the Earth? Include the appropriate sign.
    Work done by Earth = ............Joules

    (b) At the instant in part (a) when the mass has moved downward a distance of 0.09 m, the speed of the mass has decreased to 2.13 m/s. How much work was done on the mass by the spring? Include the appropriate sign.
    Work done by spring = ............Joules
    3. The attempt at a solution
    To calculate Work I'm using the formula F times displacement
    So for (a) I calculated:
    0.09m X -9.8m/s/s X 0.091kg = -0.080262J
    is that correct?
    For part B I have no idea what to do?
    Thanks if you can help.
  2. jcsd
  3. Apr 24, 2010 #2
    Part B mainly requires for you to calculate the difference in the kinetic energy.
  4. Apr 24, 2010 #3

    Doc Al

    User Avatar

    Staff: Mentor

    Except for the sign. What determines the sign of the work done is whether the force and displacement are in the same direction or not. If they are, the work done is positive.
    What's the net work done on the mass?
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