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Homework Help: Power, velocity and frictional resistance

  1. Nov 20, 2012 #1
    1. The problem statement, all variables and given/known data
    (a) A car of mass 1365kg has 60kW engine and a max speed of 145km/hr. Find the frictional resistance.

    (b) Calculate max speed of car up a gradient of 1 in 5 if Friction stays the same.

    2. Relevant equations

    P = F.v

    3. The attempt at a solution

    60000 = F (40.2m/s)
    F = 149205 N

    (b) P = netF . V
    60000 = (1492.5 + mgsinθ)
    θ = angle of inclination
    60000 = [1492.5 + (1365)(9.8)(1/[itex]\sqrt{26}[/itex])]V
    v = 60000/4118.6 = 14056 m/s

    Is this correct?
  2. jcsd
  3. Nov 20, 2012 #2


    User Avatar
    Homework Helper

    It looks good to me!

    The question isn't quite right; friction will not remain the same as the speed changes.
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