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The speed of a goods truck which has been shunted on to a level siding falls from 10km/h to 5km/h in moving a distance of 30m. If the retardation is constant, how much further will the truck travel before coming to to rest?

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  1. 10 km/h * 1000/3600 = 2.78 m/s
    5 km/h = 1.39 m/s

    v = V i + a t
    1.39 = 2.78 + a t
    so
    a = -1.39/t
    x = Xi + Vi t + (1/2) a t^2
    30 = 0 + 2.78 t - 0.694 t = 2.09 t
    t = 14.4 seconds
    a = -1.39/14.4 = - 0.0965 m/s^2
    x = average speed during stop * time to stop
    average speed = 1.39/2= 0.695 m/s
    0 = 1.39 - 0.0965t
    t = 14.4 s
    x = 0.695 * 14.4
    = 10 meters

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