f.4 phys,,,running..
2008-10-13 1:16 am
In a 100m dash, a sprinter accelerates from rest to the top speed with an average acceleration of 4ms^-2. He keeps running at the top speed and crosses the finish line 11s after he starts. Determine his top speed and the time at which he attain the top speed.
回答 (1)
2008-10-13 2:20 am
✔ 最佳答案
Let v be the top speed of the sprinter.Consider the journey when he is accelerating:
By v = u + at
v = 0 + 4t
v = 4t
By s = ut + 1/2 at2
s = 0 + 1/2 (4)t2
s = 2t2
Consider the journey when he is running with uniform speed
Distance travelled = 100 - s
i.e. 100 - s = v(11 - t)
100 - 2t2 = 4t(11 - t)
t2 - 22t + 50 = 0
t = 2.574 s or 19.4 (rejected)
So, the time is 2.574 s when he attains the top speed
The top speed, v = 4(2.574) = 10.30 ms-1
參考: Myself~~~
收錄日期: 2021-04-13 16:09:08
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