Force needed to pull a block up an incline.

  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. Kurdt

    Kurdt 4,941
    Staff Emeritus
    Science Advisor
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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. 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. Kurdt

    Kurdt 4,941
    Staff Emeritus
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    So what force is needed to make them balance?
     
  6. 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. Kurdt

    Kurdt 4,941
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    What direction will the friction be acting in if the box is being pulled up the slope?
     
  8. mukundpa

    mukundpa 507
    Homework Helper

    What is the direction of the force applied and whether the friction will depend on that direction.
     
  9. mukundpa

    mukundpa 507
    Homework Helper

    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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