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Mechanics - Resolving Forces

  1. Feb 22, 2012 #1
    1. The problem statement, all variables and given/known data


    I'm struggling with question 6 and 7 on this exercise. I have no idea where to start so basic help would be needed to get me started.

  2. jcsd
  3. Feb 22, 2012 #2
    In what direction would the normal reaction force by the planes act?
    Can you resolve the weight vector to make sure that it balances the normal reaction vector?
  4. Feb 22, 2012 #3


    Staff: Mentor

    need diagrams and need you to show your work before we can help.
  5. Feb 22, 2012 #4


    User Avatar
    Gold Member

    I don't see any reason not to type up that question, other than if you were including a diagram which you didn't anyway. If you're going to ask people for help you could at least make it as easy to help as possible instead of making us all crane our necks with a sideways photograph...
  6. Feb 22, 2012 #5
    Here's a better pic.


    For question 6, I need to go about finding the normal contact forces P and Q. How do I do that with the info I know?
  7. Feb 22, 2012 #6
    Try finding the angles between the vectors, then resolve the "2g" vector using trigonometry in such a way that the vectors balance each other out.
  8. Feb 22, 2012 #7
    No idea how to do that,
  9. Feb 22, 2012 #8


    Staff: Mentor

    well what is the angle of P relative to the horizontal? 40 degrees plus 90 degrees right?
  10. Feb 22, 2012 #9
    No good. I need full method.
  11. Feb 22, 2012 #10


    Staff: Mentor

    sorry we cant give you the answer you have to work it out for yourself. you can show us the work and we'll tell you where you went wrong.
  12. Feb 22, 2012 #11
    resolve horizontally, to get an equation for P in terms of Q, let it be (1).

    Now resolve vertically, to get another equation in terms of P and Q. Now substitute (1) in this equation to find Q.

    So have now got Q, with this i can easily find P by substituting the value of Q in any of the equation.

    And as i said before, i don't know if it is the right way, because i haven't came across such a question before.
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