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Homework Help: Forces problemfind effective weight of mass (3 masses)

  1. Feb 11, 2010 #1
    1. The problem statement, all variables and given/known data
    http://i50.tinypic.com/r8gfba.png

    ^That is the image I got in class

    m1=500kg
    m2=1500kg
    m3=10kg
    f1=600n
    angle near f1=25 degrees
    coefficient of kinetic friction=.25

    Find effective weight of m3 in side of elevator
    Find force required to keep the elevator at constant velocity
    2. Relevant equations
    All I know is Ft=ft for both
    I have a feeling f1 is either sin25(600) or cos25(600)..I don't know what 'effective weight' really means


    3. The attempt at a solution

    Would m1 just be 9.81(500) since it's going straight up and down..does Fn=Fg here?

    For the second part, I know I probably have to set a to zero, but I can't do that when I don't know where to start
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 11, 2010 #2
    Effective weight is the apparent weight of the object. Imagine you're standing in the elevator and it's moving up very fast. You are going feel heavier than if the elevator was not moving. If the elevator is moving down you will feel lighter.

    Draw your fdb and then find acceleration.
     
  4. Feb 12, 2010 #3
    I don't understand why the angle next to F1 is there, or why there is even an F1. What is it exactly? I can't attempt to find the overall force when I don't know what to do with that.

    so, I think f1=253.6 N

    For M2, is it (.25)(sin25)(1500)=ma

    m1 is (9.81)(-500)=ma

    and I combine? or do I add F1 to M2 first..or am I completely wrong?
     
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