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Homework Help: What is the initial deceleration of the impala?

  1. Mar 27, 2017 #1
    1. The problem statement, all variables and given/known data
    On a particularly hot day at the racetrack, Dale Earnhardt's famous no. 88 Chevy impala (m = 1600 kg ) speeding at 200 mph (89 m/s) blows a gasket and the engine begins to deaccelerate.

    The car is shifted to neutral and coasts toward the pit lane. Neglecting all sources of friction and assuming the drag coeffecient is .330 and the cars frontal area = 2.76 m^2, what is the initial deacceleration of the Impala? report answer to three sig figs.

    2. Relevant equations
    [itex] F_d = (1/2)C\rho Av^2 [/itex]
    where C = drag constant, rho = density, A = surface area, v = velocity

    3. The attempt at a solution

    Well I don't have a big OP to write, I'll just use this thread for asking questions on this problem since one thing confused me from the start:

    How am I suppose to find density?

    I set up a diagram showing all of the forces, and I have Fg and Fn. It says the car was speeding at 89 m/s, im pretty sure this means its a constant speed, which means acceleration was 0. So there is no force pointing in the + x direction. There is a drag force in the - direction though, which makes sense because it's slowing down.

    How am I suppose to find the (de)acceleration though if I'm not given the density? I don't know any possible way I would be able to calculate the density of the car..
  2. jcsd
  3. Mar 27, 2017 #2
    Never mind guys. I found the density at the front page on my book -_-. I got the right answer which was 2.72 m/s^2
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