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Kinematics about ramp

  1. Feb 1, 2010 #1
    1. The problem statement, all variables and given/known data
    A sack of weight 600 N is being loaded on to a truck up a ramp inclined at 18o to the horizontal. A rope attached to the sack is held at an angle of 25o to the ramp. The coefficient of friction between the sack and the ramp is 0.3. What tension in the rope is needed:
    a. To prevent the sack from sliding down the ramp.
    b. To pull the sack up the ramp at a steady speed



    2. Relevant equations
    F = ma


    3. The attempt at a solution
    The manual wrote the answer for (a) is 18.2 N. I can't find it. My work for (a) :

    W sin 18o = T cos 25o

    T = 204.6 N

    What am I missing ?

    Thanks
     
  2. jcsd
  3. Feb 1, 2010 #2

    rl.bhat

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    Homework Helper

    You have not taken into account the frictional force while calculating T.
     
  4. Feb 1, 2010 #3
    Hi rl.bhat

    Oh my god...I thought there is no friction because it didn't move. That was a very stupid mistake. Thanks a lot !!
     
  5. Feb 1, 2010 #4

    radou

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    Homework Helper

    Of course there is - it's called static friction.
     
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