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Homework Help: Torque problem

  1. Oct 30, 2016 #1
    1. The problem statement, all variables and given/known data
    When a wood shelf of mass 7.7 kg is fastened inside a slot in a vertical support as shown in (Figure 1) , the support exerts a torque on the shelf. Assume that the slot exerts two vertical forces on the shelf, at points A and B.
    Determine the force exerted on the shelf by the support slot at A.

    2. Relevant equations

    3. The attempt at a solution
    I know that the sum of the torques has to equal 0 and that the forces at A and CM is downwards, and upwards at B but I can't seem to get the correct answer (the correct answer is -566N)
  2. jcsd
  3. Oct 30, 2016 #2
    What did you get for an answer?

    Edit: I didn't get that answer either. But I don't have a lot of confidence in my answer because I know from experience that I make lots of mistakes. :)
    Last edited: Oct 30, 2016
  4. Oct 30, 2016 #3


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    I got the "right" answer. Use g=9.8 not 9.81 or 10.
  5. Oct 30, 2016 #4
    Thanks @CWatters. Because of your post, I want back and reviewed my work and found my mistake. My mistake was greater than what would be caused by using different gravity values. And yes, 9.8 gives the right answer.
  6. Oct 30, 2016 #5


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    Please post your working. A bit hard to find your mistake otherwise.
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