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Determining the energy of an object

  1. Oct 6, 2009 #1
    I'm having some trouble with some relatively basic Simple Harmonic Motion problems.

    First off, when determining the energy of an object do we need to take into account it's height of above the ground? At t=0 it is at 0.50m(highest) and at t=0.5 it's at 0.10m (it's lowest). The maximum velocity would take place at 0.3m, would I have to take into account the potential energy it has from just hanging there or do I just take into account it's energy from it's velocity?

    Also what does this "5. What is the value of the frequency in Hz (no units with your answer) where you expect to see a maximum in the amplitude for your sketch of amplitude of the motion of the object as a function of frequency." even mean. I have no idea what the question is even asking.

    Thanks in advance.
     
  2. jcsd
  3. Oct 6, 2009 #2
    Yes the height is needed. It provides the potential energy of the pendulum. The max. velocity is actually at the bottom. At .5m(the top) it is not moving so all the energy is potential. At the bottom, it has no potential, hence being at the bottom so all its energy is in kinetic form. Given you know the Δh, you can find the potential. Assuming it is a closed system the potential at the top is equal to the max. kinetic energy at the bottom.

    I think the sketch you are talking about is a graph of Amplitude vs. time. The amplitude being the max. velocity seems like. Hopefully you know what this graph looks like :)

    Hope this helps...correct me if I'm wrong please :D
     
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