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Trying to understand the solution given

  1. Jan 1, 2015 #1
    Hello, following is the mechanics problem involving pulley from an engineering mechanics book. I am trying to understand the solution given. As the car is being pulled, upward of the incline is assumed to be positive x direction. But when they apply the relative acceleration equation, in eq 3, the acceleration of the point P with respect to the car is entered as +4. Since the acceleration of the point P with respect to the car is acting downward the incline, this should be entered as -4 in equation 3. What people here think ? I have attached the problem and its solution as the PNG image file. problem.png



    thank you
     
  2. jcsd
  3. Jan 1, 2015 #2

    haruspex

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    Read it more carefully. It says the position and acceleration of the car are measured down the plane.
     
  4. Jan 18, 2015 #3
    Hello haruspex, sorry for late reply. But where is the statement which says that position and acceleration are measured down the plane ? If you look at the picture of the axes given in the solution, positive x axis is point upward the incline.....
     
  5. Jan 18, 2015 #4

    jtbell

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    Look at the direction of the arrows in diagram (b).
     
  6. Jan 18, 2015 #5

    haruspex

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    Second sentence in the paragraph headed "free body diagram"
     
  7. Jan 18, 2015 #6
    yes, I see now. thanks both of you.
     
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