Trying to understand the solution given

  • #1
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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
 

Answers and Replies

  • #2
haruspex
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Read it more carefully. It says the position and acceleration of the car are measured down the plane.
 
  • #3
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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.....
 
  • #4
jtbell
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Look at the direction of the arrows in diagram (b).
 
  • #5
haruspex
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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.....
Second sentence in the paragraph headed "free body diagram"
 
  • #6
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yes, I see now. thanks both of you.
 

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