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Acceleration and Force

  1. Oct 20, 2008 #1
    1. The problem statement, all variables and given/known data

    A 50-kg crate is pulled across the ice with a rope. A force of 80 N is applied at an angle of 36° with the horizontal. Neglecting friction, calculate

    (a) the acceleration of the crate.
    (b) the upward force the ice exerts on the crate as it is pulled.

    2. Relevant equations

    law of Cosines
    law of sines

    3. The attempt at a solution

    I have the upward force "Fay" which is 443N
    using the law of sines 80sin36 = 443N which is the vertical force and usig the law of cosines the horizontal is 64.72N

    I am not sure how to calculate the acceleration
  2. jcsd
  3. Oct 20, 2008 #2


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    Homework Helper

    Use F=ma. What is the force acting on the crate in the horizontal direction? That is the force that is causing the crate to accelerate.
  4. Oct 20, 2008 #3
    oh wow thanks
    so you use the "horizontal" force and with F=ma
    the horizontal force of 64.72=50kg *a
    it becomes 1.2944m/s

    So you would always use the horizontal force to the ground for accleration or only in this case?
  5. Oct 20, 2008 #4


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    Homework Helper

    Since the crate is only moving in the horizontal direction (so it isn't rising falling - it stays in constant contact with the ice) the acceleration is only in the horizontal direction. I wouldn't say you always use the horizontal force, it depends on the situation.
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