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Homework Help: Verification: Hanging mass on cylinder. Moment of inertia

  1. May 1, 2010 #1
    1. The problem statement, all variables and given/known data
    A 15.0 kg bucket of water is suspended by a very light rope wrapped around a solid cylinder 0.300 m in diameter with a mass of 12.0 kg. The cylinder pivots on a frictionless axle through its centre. The bucket is released from rest at the top of a well and falls 10.0 m to the water.
    a) What is the tension in the rope while the bucket is falling? my answer: 42.15N
    b) With what speed does the bucket strike the water? my answer: 11.8m/s
    c) What is the time of the fall? my answer: 1.69s
    d) While the bucket is falling, what is the force exerted on the cylinder by the axle: my answer: 159.87N this is the one that i am really unsure of (and a))

    2. Relevant equations

    solved but unsure

    3. The attempt at a solution

    could someone who knows what there doing please check my answers, i wouldn't ask if it wasn't important.. thanks in advance.
  2. jcsd
  3. May 1, 2010 #2


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    It looks good. How did you get the force of the axle?

  4. May 1, 2010 #3
    actually that part was wrong, it is actually just F=ma and it turns out to be 105N i hope. ive actually been getting a lot of help from someone else on PF
  5. May 1, 2010 #4
    Hi, just a quick question. why do they give the radius of the cylinder if it is not needed, is there a way to solve these problems that does require the radius?
    I have another very similar problem to this that i didnt use the radius for either
  6. May 1, 2010 #5
    They could be giving you extra info for you to sift through and see what's relevant and what's not.
  7. May 1, 2010 #6


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    Gold Member

    If the problem gave you a pulley with a moment of inertia that cannot be calculated from a formula, then you do need the radius. However, the method is the same.
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