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Homework Help: How to calculate the work done by the system

  1. Feb 17, 2009 #1
    HI I have some problem in calculation of the work dony by system.
    the problem is i have one oscillatory mechanical system. For this system we r applying periodic force sinusoidally. for this system at entry and exit we are measuring the displacement signal and force signal. at resonance frequency the out put displacement and force signal is much higher than at input values. I am calculating the workd done at input and out put based on the formula W=|F|*|dx| based on this formula i am getting more work at output than input ,, is it mean that our system efficiency is more than 100%..
    i am confusing where i am doing mistake.. can some one help me in this..
  2. jcsd
  3. Feb 17, 2009 #2
    Hi, welcome to the forums. Your question is a little vague; may I ask that you supply a few more details? Specifically, can you explain precisely what kind of "oscillatory mechanical system" you are referring to? How does it work? What exact methods are you employing to measure the device's input and output force/work, and with what equipment? Don't worry about writing "too much" -- people here like a puzzle, but you need to supply more pieces before we have a chance of solving it!
  4. Feb 17, 2009 #3
    You can think about the other energy sources in the system.I am not confirm, but this is one of the mistake that I do.
  5. Feb 18, 2009 #4
    Hi Thanyou for your reply. I am giving the clear description of our system.

    our system is consisting of more than twenty springs compressed and fixed in between two couplings. one end of this coupling is made fixed to the LDS vibrator and another end of this coupling is fixed to some mass(M). This LDS linear vibrator is going to give periodic force to this system and the system is going to oscilate to and fro around mean position like linear vibrator.we are measuring the force and displacement given to the system at input and force and displacement of the sytem at output using standard position sensor and force meter. During this process we are changing the frequency of the input force(vibrator) such that it should be equal to the resonance frequecny . after reaching this resonance frequency we observed as force and displament signals are out put and input.
    main observation is out put signals both displacement and force is much higher than the input values. we are calculating the work at input and out put using the formula W=|F|*|dx| and summing up all these values for one period and calculating the power using W/T here T=period of the signal or T=1/f , f= frequency of the signal.
    we observed that output power is allmost 20 times the input power and we are claiming as this sytem efficieny is more than 100% and amplifying the energy so it can be used as enery generator.
    i am very confused here.. is this the way of calculation of work done is correct or wrong?
    i am very eagerly want to know ur comments.

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