Force needed to pull a block up an incline.

  1. Sep 30, 2009 #1
    1. The problem statement, all variables and given/known data
    Calculate the force needed to pull a mass of 20 kg at a uniform slow speed up a plane inclined at an angle of 30 with the horizontal if the coefficient of kinetic friction is 0.20.

    2. Relevant equations
    WN= w cos [tex]\vartheta[/tex]
    WT= w sin [tex]\vartheta[/tex]
    [tex]\mu[/tex]s= tan[tex]\vartheta[/tex]

    3. The attempt at a solution

    I don't even know how to get started.
     
  2. jcsd
  3. Sep 30, 2009 #2

    Kurdt

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    If the block is moving at a constant speed then you know that there is no net force acting on the block.
     
    Last edited: Oct 2, 2009
  4. Sep 30, 2009 #3
    so the friction force is
    (.2)(20)(9.8)(cos 30) ?

    and the gravitational force is
    (20)(9.8)(sin 30) ?

    i got 34 N for friction and 98 N for gravitational.

    are they supposed to equal zero? or do i add them together to find the force i need to overcome? or could i just overcome the strongest?
     
  5. Oct 1, 2009 #4

    Kurdt

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    So what force is needed to make them balance?
     
  6. Oct 1, 2009 #5
    okay, so 34 N for friction pull the box up the slope, and 98 N gravity pull down.

    98 N - 34 N = 64 N needed to equalize them, and more than 64 to make it move uphill?
     
  7. Oct 2, 2009 #6

    Kurdt

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    What direction will the friction be acting in if the box is being pulled up the slope?
     
  8. Oct 2, 2009 #7

    mukundpa

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    What is the direction of the force applied and whether the friction will depend on that direction.
     
  9. Oct 2, 2009 #8

    mukundpa

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    If the minimum force needed is required than the force must be applied at an angle equal to angle of friction [tan^-1 (u)] with the incline.
     
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