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Drag racing

  1. Jun 1, 2004 #1
    i have a few formula for my physics assignment but i want to know the best way to set it out and what other formula i can use.

    i already have the formula f=m*a and a=(v-u)/t.
    i just really need the marks
     
  2. jcsd
  3. Jun 1, 2004 #2
    Perhaps if you described what the assignment requires we would be of more help? You probably need a good grasp of mechanics, and that includes the formulas you list as well as some more. Here are just a few:

    [tex]x(t) = x_0 + v_0t + \frac{1}{2}at^2[/tex]
    [tex]v(t) = v_0 + at[/tex]
    [tex]v = \frac{dx}{dt}[/tex]
    [tex]a = \frac{dv}{dt}[/tex]
    [tex]\Sigma F = ma[/tex]

    This might also be helpful:
    http://hyperphysics.phy-astr.gsu.edu/hbase/mot.html#motcon
     
  4. Jun 1, 2004 #3
    s = ut + 1/2 a t^2

    For drag racing, u is zero. s is 1/4 mile (usually) (402.336 metres) so you get

    402.336 = a/2 * t^2

    t = sqrt(804.672 / a)

    So you see that 1g (g = 9.81) acceleration will give you a 9 second run
    or 5g would give a 4 second run

    Real dragsters don't accelerate at a constant rate, but these formulae are ok as approximations.
     
  5. Jun 1, 2004 #4
    You assume that the car accelerates not only constantly, but also throughout the race. Who's to say the car doesn't top at some value of V and proceeds with no acceleration at all?
     
  6. Jun 1, 2004 #5

    krab

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    Science Advisor

    Usually, car is first traction-limited, in which case, applied force F is constant:
    [tex]mdv/dt=F-Cv^2[/tex]
    At some point, it becomes power -limited with P constant:
    [tex]mdv/dt=P/v-Cv^2[/tex]
    C is aerodynamic drag coefficient. Aero drag is much more important than rolling resistance, so I ignore a [itex]C_2v[/itex] term.
    BTW, you will notice that C can be derived from top speed [itex]v_\infty[/itex] (where dv/dt=0):
    [tex]C=P/v_\infty^3[/tex]
     
    Last edited: Jun 1, 2004
  7. Jun 3, 2004 #6
    thank you this helps
     
  8. Jun 3, 2004 #7
    when that happens you
    A shift a gear
    or if in top gear

    B change final drive gears

    but very few cars will do that in top gear
    ie reach top speed in less than a 1/4 mile
     
  9. Jun 6, 2004 #8
    ray b has it. If the car reaches maximum speed before it hits the traps, the mechanics will work the car over by changing the gears in the rear-end.
     
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