Physics

When you try to stop your car in an emergency, there is some time before you can react.Your car is going 25 m/s and your reaction time is 0.20 s, then after you hit your brakes it decelerates at 9.5 m/s2. How far will your car travel before it stops?

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  1. It takes t = 25/9.5 seconds to stop once the brakes are applied.
    s = 25*0.2 + 25t - 4.75 t^2 is the total stopping distance

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    oobleck
  2. d = 25 * 0.20 + x = 5 + x
    x = (25/2) t = (1/2) a t^2
    a t = 25
    9.5 t = 25
    t = 25/9.5 = 2.63 seconds braking
    x = (25/2) (2.63) = 32.9
    so
    d = 5 + 32. 9 = 37.9 meters
    ==========================
    check
    v = a t
    v = 9.5 * 2.63 = 25 check
    x = 12.5 t = 12.5*2.63 = 32.9 check
    32.9 + 25*.2 = 37.9 check

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    Damon
  3. d1 = V*T = 25*0.2 = 5 m. = distance traveled during reaction time.

    V^2 = Vo^2+2a*d2 = 0
    25^2-19*d2 = 0
    d2 = 33 m. = distance traveled during deceleration.

    d = d1+d2 = 5+33 = 38 m.

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