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Homework Help: Double plane fiction

  1. Sep 27, 2005 #1
    In this problem I'm asked to find the acceleration in the positive x direction.

    How do you solve problems like this? I solved one earlier just like this except sans friction and I used (and it worked)

    a = (m1g sin(alpha) - m2g sin (beta))/(m1+m2)

    so for this one I tried a = ((m1g sin(alpha) - m1(mu)g cos(alpha)) - (m2g sin (beta) - m2(mu)g cos(beta))/(m1+m2)

    I think the problem is that I didn't include the tension of the other block when finding a blocks normal force, but I'm not sure how to go about finding this.

    Also, In our text, for a mass hanging straight down held by a string, it gives the equation Tension - mg = -ma

    does this just mean that the force of tension minus the force of gravity equals the total acceleration of the mass?

    Much thanks to anyone who contributes some advice or direction.

    the diagram
  2. jcsd
  3. Sep 28, 2005 #2
    anybody? on either question?
  4. Sep 28, 2005 #3


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    No need to add tension in the normal reaction because it is tangential. Looks good.

    Ind second why -ma ? If a is unknown you will get the correct sign automatically, only + acc. will be upward.
  5. Sep 28, 2005 #4
    that's what i thought, but that's whats in the text
  6. Sep 29, 2005 #5


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    If there is no any other reference it looks odd.
    Even then before considering it wrong show it to your prof.
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