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Homework Help: Power supplied holding a mass suspended in air

  1. May 25, 2014 #1
    A problem I thought would be very simple, but can't seem to get very far with.

    Taking equations from textbook: Fv = P . Nope because velocity is 0 however power cannot be 0.
    Using suvat: W = Fs , s = ut + .5gt^t , therefore P = Fgt/2 , this seems like the equation for how power would increase as an object falls but not the power supplied to keep it suspended which I imagine would be constant with time.

    So there it is, leaving me very fustrated as it seems like it must be really simple.
  2. jcsd
  3. May 25, 2014 #2


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    Yes. Power=Fv and if it's velocity is changing(Accelerating at g), it's power should also change.

    I don't think I understood you r question clearly. We don't need power,not even energy to hold things in place. Consider a book lying at rest on a table. No work is done there.

    Edit. You can still use that equation. Since no distance is travelled when it's suspended, you can just plug in 0 into s in P=Fs/t
  4. May 25, 2014 #3
    Ok but hold 50 kilos out in front of you and tell my why its tiring but no work is being done?
  5. May 25, 2014 #4


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    Tiring and work done are two different things.
    Our bodies are not efficient. We even get tired sitting somewhere without moving.
    Muscle cells in our body need constant supply of energy to stay contracted(Which keeps things lifted up) On the other hand, the table does not deform to keep things above the ground.
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