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5 June, 17:48

A 384 m long train is moving on a straight track with a speed of 77.3 km/h. The engineer applies the brakes at a crossing, and later the back of the last car passing the crossing with a speed of 19.5 km/h. Assuming constant acceleration, determine how long the train blocked the crossway. Disregard the width of the crossing. Convert the time into three different units: s, min, and hr.

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  1. 5 June, 18:25
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    The time the train blocked the crossway is

    0.007934h=0.476 min=28.6 s

    Explanation:

    The average speed is given by

    V = (Vi+Vf) / 2

    and

    V = dx/dt

    Where

    Vi = initial speed

    Vf = final speed

    dx = change of position=0.384 km

    dt=time the train blocked the crossway

    dt=2dx / (Vi+Vf)

    dt=2*0.384 km / (77.3 + 19.5) km/h

    dt=0.007934h

    dt=0.007934h * (60min/1h) = 0.476 min

    dt=0.476 min * (60s/1min) = 28.6 s
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