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Homework Help: Derive an expression for the tension in the cord

  1. Apr 6, 2008 #1
    A rock with mass m = 3.10 kg is suspended from the roof of an elevator by a light cord. The rock is totally immersed in a bucket of water that sits on the floor of the elevator, but the rock doesn't touch the bottom or sides of the bucket.

    Here is the part that I am stuck on:
    Derive an expression for the tension in the cord when the elevator is accelerating upward with an acceleration of magnitude a .

    I have concluded that
    Tension=m(g-a)-1000V(g-a)

    Or force of the body-force of the water displaced but it is incorrect.
     
  2. jcsd
  3. Apr 7, 2008 #2
    For an observer in elevator, rock is in equilibrium. Net force is zero.

    m(g+a)-(T+F)=0

    mg-ma-T-F=0

    T=mg-(ma+F)

    mg: weight
    ma: inertia force
    T: tension
    F: the lift of water
     
  4. Apr 7, 2008 #3

    Doc Al

    User Avatar

    Staff: Mentor

    Show how you arrived at this answer. (How does the acceleration of the elevator affect the buoyant force?)
     
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