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Homework Help: Two masses on an inclined plane

  1. Aug 10, 2009 #1
    Hi, how would i go about finding/resolving forces on an inclined plane with one mass on top of another?
    Friction is neglected between the mass and the plane. But you need to find the minimum allowable coefficient of friction between the two blocks.

    the incline is at 30 degrees
    block a on the incline is 40kg
    block b, which is on block a is 10kg
    there is also a 500N force on block a being pulled up the plane parallel to the plane

    Thankyou in advance
  2. jcsd
  3. Aug 10, 2009 #2
    For future reference, please use the boldface categories to write the problem down (problem statement, relevant equations, attempt at solution). It makes the question more clear for you and everyone that might help you out.

    If you can do regular inclined planes then a problem with a mass sitting on top of another is a piece of cake if you think about it properly. For this problem you can think about the two masses as point particles, with point b on top of a. If b has a smaller acceleration (or velocity) than a, b is going to fall off right? So the acceleration of b is going to be the same as a. It shouldn't be too hard from there to find the forces acting on the two masses and solve for Mu between them.
  4. Feb 16, 2011 #3
    you need to show some of your efforts on the question so that we may solve the problems you are having. you dont just want us to solve the question and present it to you. do you?
  5. Feb 16, 2011 #4


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    I suspect the OP has lost interest in solving this problem by now.
  6. Feb 17, 2011 #5
    what do you mean by OP
  7. Feb 17, 2011 #6
    (I assume that the plane is supposed to be motionless?)

    Try drawing a picture of the problem: draw the inclined plane, the two masses on it, and then, add all the relevant forces (in projection form). Then write the equations for Newton's second law for the bodies - in projection form.

    If you do this right, the problem should be solved easily.
  8. Feb 17, 2011 #7


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    "OP" means "original poster", or the person who started this thread.

    Look at the date that Post #1 was made.
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