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Applying the work-energy theorem

  1. Oct 15, 2008 #1
    1. The problem statement, all variables and given/known data
    Use the work-energy theorem to solve.
    A branch falls from the top of a 95 m tall tree, starting from rest. How fast is it moving when it reaches the ground? Neglect air resistance.

    2. Relevant equations
    work-energy theorem:w_total=K_2-K_1
    In this problem, K_1 is 0 since it is starting from rest.
    K_2=(1/2)*m*v^2 (?)
    w=fd (relevant?)

    3. The attempt at a solution
    If I use the equations I have above, I end up with w=1/2*m*v_f^2.
    However, I am not given a mass. I do not know how to finish the calculation without a mass.
    If I use w=fd, I have (9.8 m/s^2)(mass)*(95 m).
    I am really stuck.
     
  2. jcsd
  3. Oct 16, 2008 #2

    atyy

    User Avatar
    Science Advisor

    In addition to the equations you listed, you also need the equation for the force of gravity on a mass.

    You are only asked for the final velocity. Assume a mass, and carry through with the equations. Hopefully the mass will cancel out when you solve for the velocity.
     
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