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An engineer in a locomotive sees a car stuck on the track at a railroad crossing in front of the train. When the engineer first sees thecar, the locomotive is 310 m from the crossingand its speed is 10 m/s.If the engineer’s reaction time is 0.39 s,what should be the magnitude of the minimum deceleration to avoid an accident?Answer in units of m/s2.

  • physics -

    D = 310 m -10m/s *0.39s = 306.1 m
    after reaction time.

    D = v * t
    306.1 = 10m/s * t
    t = 30.61s = time to reach stalled car.
    Deceleration must reduce velocity to
    0 in 30.6 s or less.

    Deceleration = (Vt - Vo) / t =
    (0 - 10m/s) / 30.61s = -0.327m/s^2.

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