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Pulley problem

  1. May 18, 2017 #1
    1. The problem statement, all variables and given/known data
    There's two blocks of mass m_{A} and m_{B} which are linked by an ideal string. The block of mass A descends at constant speed. There's no friction. If the pulley is ideal, which one of the following is true

    upload_2017-5-19_0-33-15.png
    2. Relevant equations
    Newton laws and trigonometry I think.



    3. The attempt at a solution
    I think that the correct answer is the second one, but the first one is marked as correct so I wanted a second opinion.
    My reasoning is the following: If the speed is constant it means there is no acceleration, so the sum of the forces is 0. Then I decomposed gravity in the component that's compensated by the normal force done by the triangle and it's perpendicular component. So I arrived to
    m_{A} (1/2) = m_{B} sqrt(3)/2
    Now that I check, it isn't item 2. it would fall in item 1 as 1/sqrt(3) is between 0.25 and 0.6
    Right?

    sorry for the typos, I broke my keyboard yesterday (I won't drink coffee while on computer again) and I'm with a rubber one until a new one arrives, at least it's better thanthe one that windows have to use with the mouse.

     

    Attached Files:

  2. jcsd
  3. May 18, 2017 #2
    Working it out very quickly, and thus prone to error, I think the first answer is correct.
     
  4. May 18, 2017 #3

    haruspex

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    Yes.
     
  5. May 19, 2017 #4
    Absolutely correct! Way of solving by simply taking their Sine components of 'g' and solve it.
     
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