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Homework Help: How to find acceleration from only initial and final velocity

  1. Mar 13, 2013 #1
    1. The problem statement, all variables and given/known data
    A novice snowboarder who weighs 60kg is sliding down a 10 degree slope at a constant velocity of 8 m.s^-1.
    When they reach the bottom of the slope, they slow down due to the kinetic friction between the snowboard and the snow.

    Find the rate at which the skier is de accelerating once they are on the flat snow.

    2. Relevant equations

    3. The attempt at a solution

    I found the coefficient of kinetic friction (0.176), but how can you calculate the rate of de acceleration?
    Last edited: Mar 13, 2013
  2. jcsd
  3. Mar 13, 2013 #2
    How did you find the coefficient of friction?
  4. Mar 13, 2013 #3
    Coefficient = force of friction / normal force?
    Is that not right?
  5. Mar 13, 2013 #4
    Crap just realised I left out the snowboarders weight (60kg)
  6. Mar 13, 2013 #5
    So what is the force of friction at the bottom then?
  7. Mar 13, 2013 #6
    im sorry but i dont know how I would
  8. Mar 13, 2013 #7
    You did that for the slope. Why can't you do it for the bottom?
  9. Mar 13, 2013 #8
    Isnt there no net force acting at the bottom?

    I found it on the slope because there was a force pulling it down the slope, but there isnt anything at the flat
  10. Mar 13, 2013 #9
    The net force is zero on the slope, because the acceleration is zero. At the bottom, the snowboarder decelerates, which means the net force is not zero.

    Start with the free body diagram.
  11. Mar 13, 2013 #10
    My free body diagram shows the normal force and the weight arrows, and a force acting backwards, a force I am assuming is the kinetic friction acting on the snowboarder, slowing him down.

    is that correct? where do i go from there?
  12. Mar 13, 2013 #11
    Indeed, these are the forces acting on the snowboarder. You need to determine the acceleration.
  13. Mar 13, 2013 #12
    I agree. Im just very unsure as to how i would go about that.
    Thank you so much for your help so far!
  14. Mar 13, 2013 #13
    As always, ma = net force. Decompose that into X and Y directions, and see where that gets you. This is actually simpler than what you did on the slope, there is no trigonometry involved.
  15. Mar 13, 2013 #14
    The net force would be coefficient of friction derived above, multiplied by the Normal force, yes? (but the answer would be negative as it is pointing in the negative x direction?)

    And then just solve for a?
  16. Mar 13, 2013 #15
  17. Mar 13, 2013 #16
    Thank you so much for your help! You're a life saver
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