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Acceleration, distance, and friction

  1. Sep 20, 2010 #1
    heres a problem im stuck on..can someone plz help me?

    a skater has a mass of 78 kg is pushes with a constant force of 137N for a time of 3.3 sec on the ice. the coefficient of friction of the blades against the ice is 0.007.

    1. find the skaters acceleration, taking friction into account.
    2. how fast is the skater going at the end of the push?
    3. how much distance has the skater covered during the push?

    what i first did was find acceleration
    a=f/m i got 1.74 m/s2
    now what im stuck on is part 2 and 3....is the Final Velocity and Intial Velocity zero?

    someone plz help me start off this problem :)
     
  2. jcsd
  3. Sep 20, 2010 #2

    PhanthomJay

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    When you calculated the acceleration, did you account for the friction force acting opposite the pushing force? It's a rather small number, but you should include it. Once you get the acceleration, yes, the initial velocity is 0, but to get the final velocity and distance traveled after 3.3 seconds, you need to use the kinematic motion equations for constant acceleration.
     
  4. Sep 21, 2010 #3
    how will i calculate the friction force and how is it applied?
     
  5. Sep 21, 2010 #4

    PhanthomJay

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    I would think you would have studied friction at this point. Sliding frictional forces are the product of the the kinetic friction coefficent times the Normal force (the normal force is the force perpendicular to the surface), and are always in the direction that is opposite to the direction of the relative motion between the 2 surfaces (the friction force is parallel to the surface).
     
  6. Sep 21, 2010 #5
    ok..i got that formula now...so will it be friction=(0.007)(137N)
    and i get .959
     
  7. Sep 21, 2010 #6

    PhanthomJay

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    No, the normal force is not 137 N. What is the normal force acting on the skater?
     
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