1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Drag race- avg power output

  1. Sep 26, 2009 #1
    1. The problem statement, all variables and given/known data
    A top fuel drag racer with a mass of 500.0 kg completes a quarter-mile (402 m) drag race in a time of 4.3 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.


    2. Relevant equations
    P = W/T


    3. The attempt at a solution
    P = W/T
    W=FD
    F=MA =500*26.744 = 13372
    ..plugged in for W/T ... (13372 * 402 /4.3 )/ 1000
    This has not gotten me far!
    Please help and explain!!! THANKS!!!
     
  2. jcsd
  3. Sep 26, 2009 #2

    rock.freak667

    User Avatar
    Homework Helper

    Using a kinematic equation in the first 4.3 seconds it travels 402m starting from rest, so what is its acceleration? When you get this, what is the force exerted by the car then?
     
  4. Sep 26, 2009 #3

    Delphi51

    User Avatar
    Homework Helper

    Yes, how did you get that 26.744 m/s^2? I get two different answers for the acceleration depending on whether I use the distance of 402 m in 4.3 s or the final velocity of 115 m/s in 4.3 s. I think that means the acceleration is not constant, and so you can't do the problem using the W = FD method (because the force isn't constant either).

    I suggest you start with the P = W/t but instead of W = Fd, use the final energy minus the initial energy for the W.
     
  5. Sep 26, 2009 #4
    I got acceleration by vf-v0/2.
    However I got the answer. I did P=FV for avg velocity.
    Thanks though!
     
  6. Sep 26, 2009 #5
    I think a better approach here would be to use the work-energy theorem:

    [tex]W=\Delta E_k[/tex]
     
  7. Sep 26, 2009 #6
    RoyalCat,
    I cannot see the formula u posted. please try it again
     
  8. Sep 26, 2009 #7

    Delphi51

    User Avatar
    Homework Helper

    That doesn't make sense; it gives an average velocity but not an acceleration. Wrong units for one thing.

    RoyalCat's formula says W = final energy - initial energy
    and is the same thing I suggested earlier.
     
  9. Sep 26, 2009 #8
    Sorry, my typo, I meant to say i got avg velocity by using the above equation. I got acceleration by using vf - vo/t. Using that info, i plugged it into P = FV (avg V)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Drag race- avg power output
  1. Drag race problem (Replies: 8)

  2. Drag racing problem (Replies: 2)

  3. Two cars drag racing (Replies: 3)

Loading...