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Puck on Ice

  1. Sep 20, 2013 #1
    A hockey puck on a frozen pond with an initial speed of 12.3 m/s stops after sliding a distance of 198.9 m. Calculate the average value of the coefficient of kinetic friction between the puck and the ice.

    So I started with finding the acceleration. I divided 12.3m/s by 198.9m then took the inverse (so units would go back seconds) and came up with 16.17s. So now I have Δv and Δt so I divided 12.3m/s by 16.17s to get an acceleration of .76m/s^2

    I also know that friction equals μN and that F=ma. Since N=mg and friction is the only force acting on the object, i divided the mass out. So I had μg=a, or μ=a/g. (using 9.81m/s^2 as gravity) So μ=.0774 which seemed reasonable for ice. But I dont know how to find the actual force without knowing the mass. Am I even heading in the right direction?
     
  2. jcsd
  3. Sep 20, 2013 #2

    mfb

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    Staff: Mentor

    That does not work.
    To travel 198.9m in 16.17s, it would have to travel at 12.3m/s the whole time, which is clearly not the case. You need a different approach here.

    That part is good, once you fix your acceleration value. You cannot, and do not have to, calculate the force.
     
  4. Sep 21, 2013 #3
    Then how do I find acceleration? I don't have time..
     
  5. Sep 21, 2013 #4
    But you do know lots of other things. For example, you know the initial and the final speeds. I think it's okay to assume uniform acceleration here. You probably have a list of equations for dealing with this sort of motion that look something like, for example, v = u + at.

    What you need to do is find an equation that includes the quantities that you know along with the acceleration. Then there's some algebra to find a.
     
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