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waistyle二星初級會員
2010-10-31 12:42#1
A train approaches a station and slows down steadily at 2.5ms^-2 .
The front and the end of the train pass a woman on the platform with a time lapse 4s .
If the length of the train is 40m what is its initial velocity?
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AYuMeVIP會員
2010-10-31 14:02#2
s = ut + 0.5at^2
40 = 4u + 0.5(-2.5)(4^2)
60 = 4u
u = 15ms^-1
應該是這樣?因為我用中文讀物理的-w-不太肯定有無解錯題
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雪子秀版主
2010-11-1 01:33#3
少了v
已知 u= 15m/s , v= ? , a= 2.5m/s-2 , t= 4s , s=40m
v = u + at
= 15 + 10
= 25 (m/s)
[ 本帖最後由 雪子秀 於 10-11-1 01:35 AM 編輯 ]
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AYuMeVIP會員
2010-11-1 19:55#4
哦
因為只看到what is its initial velocity 以為只需找初速._.
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雪子秀版主
2010-11-1 23:27#5
只需要知道其中3樣就可以找到公式。 (s a t):smilie_:10: