science/math

A car traveling at the speed of 30.0 m/sec encounters an emergency and comes to a complete stop. how much time will it take for the car to stop if its rate of deceleration is -4.0 m/sec

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  1. Using Calculus

    a = -4
    v = -4t + c
    when t=0 , v = 30
    30 = 0 + c
    v = -4t + 30

    s = -2t^2 + 30t + k
    when t = 0 , s = 0, so k = 0

    s = -2t^2 + 30t

    when the car stops, v = 0
    4t = 30
    t = 30/4 = 7.5 seconds

    when t = 7.5
    s = -2(7.5)^2 + 30(7.5) = 112.5 m

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    posted by Reiny

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