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March 28, 2017

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You are driving to the grocery store at 12.7 m/s. You are 108.0 m from an intersection when the traffic light turns red. Assume that your reaction time is 0.470 s and that your car brakes with constant acceleration. How far are you from the intersection when you begin to apply the brakes?

  • Physics - ,

    Well, I suppose I am to assume that you stopped in 108 meters.

    first you went 12.7*.47 = 5.97 m before your foot hit the brake.

    So the brakes must stop you in (108 -6) = 102 meters

    That is the answer you asked for.
    -----------------------------------
    The rest of the problem:
    102 = 12.7 t - (1/2) a t^2
    and
    0 = 12.7 - a t
    t = 12.7/a
    so
    102 = 12.7^2/a - (1/2) (12.7^2)/a
    204 a = 12.7^2
    a = .8 m/s^2 about a tenth of g

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