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March 25, 2017

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100 m from a traffic light, a motorist sees it to red. If he needs to accelerate at -1 m.s ^2 to stop at the traffic light, what is the initial speed, and how long did he take to stop?

  • Physics - ,

    Let initial speed = Vo
    Average speed while decelerating = Vo/2
    X = 100 m
    Time to decelerate to zero =
    T = 2 X/Vo
    also,
    T = Vo/a.
    Therefore
    2X/Vo = Vo/a
    Vo = sqrt(2 a X) = 14.1 m/s
    T = 14.1/1 = 14.1 s

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