Motion question?

[匿名]

2021-01-04 7:23 pm

A bus travels 400 m between two bus stops. It starts from rest and accelerates at 1.5 m/s^2 until it reaches a speed of 9 m/s. The bus continues its journey at this speed and then decelerates at 2.0 m/s^2 until it stops. Calculate the total time for the journey.

回答 (1)

Uncle Michael

2021-01-04 7:45 pm

✔ 最佳答案

Consider the journey for acceleration:
v² = u² + 2as                          and   v = u + at
9² = 0² + 2(1.5)s                     and   9 = 0 + 1.5t
Distance traveled, s = 27 m   and   Time taken, t = 6 s

Consider the journey for deceleration:
v² = u² + 2as                                and   v = u + at
0² = 9² + 2(-2)s                            and   9 = 0 + 2t
Distance traveled, s = 20.25 m   and   Time taken, t = 4.5 s

Consider the journey for constant speed:
Time taken = (400 - 27 - 20.25) / 9 = 39.2 s

Total time taken = 6 + 4.5 + 39.2 = 49.7 s

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