f.4 phys,,,urgent!!
2008-10-20 3:05 am
Sally is driving a car at 80kmh^-1 along a straight road and sees a police checkpoint 70m ahead. If she needs to stop just in front of the checkpoint, what is the minimum deceleration of the car? Suppose her reaction time is 1s.
回答 (1)
2008-10-20 3:13 am
✔ 最佳答案
u = 80kmh^-1 = 80/3.6 ms^-1v = 0kmh^-1 = 0ms^-1
a = ?
Stopping Distance + Breaking Distance < 70m
Stopping Distance
= 1s x 80/3.6 ms^-1
= 80/3.6 m
s = 70 - 80/3.6 m
Breaking Distance
By v^2 - u^2 = 2as
0 - (80/3.6)^2 = (2)(a)(70 - 80/3.6)
a = 5.168 ms^-2
Min deceleration = 5.168 ms^-2
參考: myself
收錄日期: 2021-04-13 16:10:27
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20081019000051KK02167