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Homework Help: Pulley with rope at angle

  1. Mar 14, 2010 #1
    1. The problem statement, all variables and given/known data

    http://s284.photobucket.com/albums/ll12/toluun/?action=view&current=IMAG0004.jpg

    Here is a picture of the problem at hand. I know how to solve the problem however the only thing I don't understand is the relationship between A and B. This means that if A moves to the right 1ft how far will B move downward?

    2. Relevant equations

    I know how to solve the problem however the only thing I don't understand is the relationship between A and B. This means that if A moves to the right 1ft how far will B move downward?


    3. The attempt at a solution

    I first tried thinking that if A moved 1 ft to the right the change in B would be the length of the rope covered. So Xb(change in mass b)= Xa/cos(30).

    However this is incorrect I have the solution and the relationship is Xb = Xa * cos(30)
    can anyone explain this?
     
  2. jcsd
  3. Mar 14, 2010 #2

    ideasrule

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    Homework Helper

    You know that r*cos(theta)=Xa and r+Xb=constant (said constant being the length of the rope). You can figure out the relationship between Xa and Xb by substitution.
     
  4. Mar 14, 2010 #3
    I have a question, since we are looking for the relationship between the accelerations, we have to differentiate to get it. But when we do, do we differentiate the cos(theta)?
     
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