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Work and Tension

  1. Aug 6, 2008 #1
    1. The problem statement, all variables and given/known data

    There is a block with a mass of 4kg attached to a rope where tension is point upwards. The block is lowered by the rope, and the tension is 35N. If block is lowered 10m:

    A) What is work done by the rope?
    B) What is delta K.E.?

    2. Relevant equations

    W = mgh
    W = Fd

    3. The attempt at a solution

    A) W = Fd = -350J

    I am having a hard time with the concept as to why the block does not affect the work on the rope. Also, how is the block losing energy (indicated by the negative sign in the solution)?

    B) Can I solve it this way:

    Fd = delta U + delta K

    (35)(10) = (4)(10)(10) + delta K

    -50J = delta K
     
    Last edited: Aug 6, 2008
  2. jcsd
  3. Aug 6, 2008 #2

    alphysicist

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    Homework Helper

    You're missing a trig factor here (which gives you the minus sign in part a).

    If you compare a block being lowered by this rope to a block that is just dropped 10m, the one that is dropped has more energy after dropping 10m.

    You have some sign errors here. You had already found in part a that the work was -350J. For the delta U term, what is delta h?
     
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