Jessica 發問於 科學及數學其他 - 科學 · 1 十年前

Physics---urgent

A boy was hit by a car when he was crossing a zebra-crossing.

Let d be the distance between the car and the boy at the moment the driver first observed the boy. The driver applied the brakes and skid mark 36.0 m long was left on the road. After hitting the boy, the car travelled a distance of 19.7 m before coming to rest. You may neglect the change in speed of the car during the impact.

更新:

1) Estimate the thinking distance and the value of d. (with steps)

2) The speed limit of the road is 50 km h^-1(i.e. 13.9 m s^-1). If the car is travelling at this speed, explain whether it would hit the boy.

1 個解答

評分
  • 1 十年前
    最愛解答

    This is a question in 2002 CE past paper 1

    1. From the graph, since u = 21.5 m/s

    So, think distance l = 15 m

    From the figure,

    19.7 + d = 36 + l

    d = 36 + 15 - 19.7

    d = 31.3 m

    2. If the car is travelling at this speed (13.9 m/s),

    the thinking distance will be approximately 15 m from the graph.

    The braking distance would be approximately 10 m

    And the stopping distance

    = 15 + 10

    = 25 m

    The stopping distance is shorter than d and hence the car will not hit the boy.

    資料來源: Myself~~~
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