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Average Power Output

  1. Sep 19, 2008 #1
    A top fuel drag racer with a mass of 600.0 kg completes a quarter-mile (402 m) drag race in a time of 4.4 s starting from rest. The car's final speed is 115 m/s. What is the engine's average power output? Neglect friction and air resistance.

    I know:
    Power = Work/ change in time
    W = Force * change in distance
    F = mass * acceleration
    Vf = Vi + at

    so i solve for a
    115 m/s = 0 m/s + a(4.4 s)
    a = 26.1364 m/s^2

    then i solve for F
    F = 600 kg * 26.1364 m/s^2
    F = 15681.8182 N

    then i solve for W
    W =15681.8182 N * 402 m
    W = 6304090.909 J

    then i solve for P
    P = 6304090.909 J / 4.4 s
    P = 1432747.934 W

    I'm supposed to answer in kW
    P = 1432.747 kW

    I don't understand why this answer is wrong!
     
  2. jcsd
  3. Sep 19, 2008 #2

    LowlyPion

    User Avatar
    Homework Helper

    Perhaps you want to consider that

    [tex]Work = \Delta KineticEnergy = \frac{m*v^2}{2} - 0[/tex]
     
  4. Sep 19, 2008 #3
    Thanks, LowlyPion!!

    I also tried to find a using Vf^2 = Vi^2 + 2ax and i got this same answer, but the equation you gave me made my life so much easier. :)

    Thanks again!!
     
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