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Another work problem help!

  1. Oct 6, 2012 #1
    Sorry for the second post, but I want to know how to solve such problem when it comes to this situation.

    1. The problem statement, all variables and given/known data

    A vertical rope is used to lower a block of mass M = 48.3 kg at a constant acceleration of magnitude a = 1.54 m/s2. Find WT, the work done by the tension in the cord if the mass moves down distance s = 2.47 m.

    2. Relevant equations

    →W = mad

    3. The attempt at a solution

    Hm... Tried to use this form:

    W = m(g - a)d

    But I'm not sure if I'm at the right path.
     
  2. jcsd
  3. Oct 6, 2012 #2
    It seems correct to me :)
    m(g-a) is the force used to reduce the block acceleration.
    then m(g-a)d is the work done..nothing else to be considered anymore from here
     
  4. Oct 6, 2012 #3

    tiny-tim

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    Science Advisor
    Homework Helper

    Hi NasuSama! :smile:
    No.

    The definition of work done is W = F "dot" d
    How did you get that equation? Did you use F = ma?

    If so, your F is correct, your d is correct, but your "dot" isn't. :wink:
     
  5. Oct 6, 2012 #4
    So W = F * d [Can't do the dot].

    I used F = ma to get the equation. What about the answer? Is it correct. You said F is correct and d is correct, right?

    My answer is around 987 J, but it's incorrect.
     
  6. Oct 6, 2012 #5
    W = m(g - a) [dot] d doesn't seem quite right.
     
  7. Oct 6, 2012 #6
    Never mind. I got the solution!
     
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