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Homework Help: 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.
    m/s2
    (b) the upward force the ice exerts on the crate as it is pulled.


    2. Relevant equations

    F=Ma
    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

    hage567

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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

    hage567

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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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