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Homework Help: Energy Question Please Help

  1. Aug 7, 2012 #1
    Energy Question!! Please Help!!

    1. The problem statement, all variables and given/known data
    A 170g hockey puck sliding at 25 m/s slows to a speed of 10 m/s in a distance of 7.5m. Determine the force of friction causing the puck to slow down.

    m=170g
    = 0.170kg
    V1 = 25 m/s
    V2= 10 m/s
    d = 7.5 m/s

    2. Relevant equations
    Kinetic Energy = (1/2)(m)(v^2)
    Work = Fd


    3. The attempt at a solution

    I'm really confused...

    Kinetic Energy 1 = (1/2)(0.170kg)(25m/s)
    = 2.125 J
    Kinetic Energy 2 = (1/2)(0.170kg)(10m/s)
    = 0.85 J

    Kinetic Energy 2 - Kinetic Energy 1
    0.85 J - 2.125 J = -1.325 J

    Work = Fd
    F = Work/d
    = -1.325/7.5m
    = -0.176666... which is wrong!

    Please help!!
     
  2. jcsd
  3. Aug 7, 2012 #2
    Re: Energy Question!! Please Help!!

    Check you equation.
    v2
     
  4. Aug 7, 2012 #3
    Re: Energy Question!! Please Help!!

    Oh duh! That was dumb of me! Thank you so much!
     
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