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Homework Help: Top speed and displacement

  1. Sep 26, 2007 #1
    1. The problem statement, all variables and given/known data

    Sam, whose mass is 80kg, takes off across level snow in his jet powered skis. The skis have a thrust of 189N and a coefficient of kinetic friction on snow of 0.1. Unfortuneately, the skis run out of fuel after only 12s.

    2. Relevant equations
    kinematic equations

    3. The attempt at a solution
    I have no idea where to even begin with this problem.
  2. jcsd
  3. Sep 27, 2007 #2


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    Homework Helper

    The problem statement is incomplete. What are you being asked to find?
  4. Sep 27, 2007 #3
    I'm sorry. The question wants to know what Sam's top speed is, and how far has Sam traveled when he finally coasts to a stop.
  5. Sep 27, 2007 #4


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    Homework Helper

    OK, here are a couple of hints. This is a two part problem. The first part is the powered motion. Use your equations of motion to find the distance and velocity at the point where power quits and those are initial conditions for the 2nd part of the problem, which is coasting to a stop.

    What are the relevant equations of motion? The need to involve mass, force, friction, etc. F=ma is a good start. Go a bit further. How does friction enter into the picture? If you haven't done it already, it REALLY helps to draw a picture and label the pertinent information.
  6. Sep 27, 2007 #5
    Here's some help if you're having trouble visualizing it.

  7. Sep 27, 2007 #6
    Ok, I got part A by using F-uk(n) = m(Ax). I got the acceleration to be 1.3815. Using that I found the velocity, which is 16.578. I am having trouble figuring part B out. I tried using Vxf^2 = Vxi^2 + 2(Ax)(delta x).
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