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Homework Help: Impulse and momentum of a sled

  1. Nov 8, 2008 #1
    1. The problem statement, all variables and given/known data
    a sled slides along a horizontal surface on which the coeffient of kinetic friction 0.25. its veocity at pt A is 8m/s at pt B its 5m/s. use impulse-momentum theorem to find how long the sled takes to travel from A to B


    2. Relevant equations
    P=J


    3. The attempt at a solution

    m(delta)v=Ft
    (delta)v=ukgt
    vf-vi=ukgt

    uk = kinetic friction coeff.

    ive gotten this far and im not sure how i'm suppoes to solve for time if theres 2 unknown varibles g and t.. is there a way i can solve for g .

    am i doing this question correctly?
     
  2. jcsd
  3. Nov 8, 2008 #2

    PhanthomJay

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    Re: impulse-momentum

    You've got it right....g is assumed to be the acceleration of gravity on earth, and is equal to 9.81m/s^2, a known value.
     
  4. Nov 8, 2008 #3
    Re: impulse-momentum

    that g is suppose to be acceleration i used the wrong symbol, it's on the x axis not the y axis
    sorry i confused you
     
  5. Nov 9, 2008 #4

    PhanthomJay

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    Re: impulse-momentum

    No, you used the correct symbol; it comes out of your correct calculation for the net force acting on the sled, which is u_k(m)(g). You are trying to solve for t, not a. If you want the acceleration in the horizontal direction, which is not called for, it's just F_net = ma, or a = (vf-vi)/t. The impulse-momentun equation is just another form of Newton's 2nd Law.
     
  6. Nov 9, 2008 #5
    Re: impulse-momentum

    oo thank you i was confused
     
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