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Mechanics: Friction

  1. Jul 13, 2015 #1
    1. The problem statement, all variables and given/known data
    screenshot_25.png

    2. Relevant equations
    F = ma
    Fk= u * Fn


    3. The attempt at a solution
    By analyzing the forces into components and applying newton's second law

    Fnet on y axis = 0
    So, Fn = mg + F2sin37 - F1sin 37 = 20 + 9 = 29 N

    on x-axis
    F = ma
    F1 cos 37 + F2 cos 37 - Ffr = ma
    F1 cos 37 + F2 cos 37 - uK * Fn = ma
    5*0.8 + 20*0.8 - 0.2*29 = 2a
    4 + 16 - 5.8 = 2a
    14.2 = 2a
    a = 7.1 m/s2


    Can you guide me to know my mistake, please?

    Thanks in adavance
     
  2. jcsd
  3. Jul 13, 2015 #2

    TSny

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    Gold Member

    Looks like you assumed the figure depicts a side view. Maybe it's an overhead view. If so, I think you should get one of the answers listed.
     
  4. Jul 13, 2015 #3
    So I find the resultant force which is:
    25*0.8 - 15*0.6 = 20 i - 9j
    Magnitude = 21.9 ~= 22 N

    Friction force is 0.2 * 20 = 4 N

    Net force = 22 - 4 = 18 N

    F = ma
    18 = 2a
    a = 9 m/s2

    thanks!
     
  5. Jul 13, 2015 #4

    TSny

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    Looks good!
     
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