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Q: A truck is moving a constant velocity of 10ms^-1. A motor-cycle, initially 75m behind the truck, starts its motion from rest a constant acceleration of 2ms^-2
(a). When will the motor-cycle overtake the truck?
(b). How fast is the motor-cycle travelling when it overtakes the truck?
(c). How far is the motor-cycle from the truck 2 seconds after the overtaking?
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2008-04-04 5:18 am
回答 (2)
2008-04-04 5:41 am
✔ 最佳答案
a. let t be the time.by s=ut+1/2at^2
10t+75=0+ 1/2x2t^2
t^2-10t-75=0
(t-15)(t+5)=0
t=15s (t=-5rejected)
b. v=u+at
v=2x15=30ms-1
c. distance travelled by the truck=2x10=20m
distance travelled by the motorcycle
=ut+1/2at^2
=30x2+1/2x2x4
=64m
the answer is 64-20=44m
2008-04-04 5:46 am
圖片參考：http://hk.geocities.com/viceleader982040/cephysics2.jpg
a)Let's after t seconds,the motor-cycle will overtake the truck
S1/10=t----(1)
a=2,u=0,S2=75+S1,t=?
by S=ut+1/2at^2
75+S1=(0.5)(2)(t^2)----(2)
subS1=10t into (2)
75+10t=t^2
t^2-10t-75=0
(t+5)(t-15)=0
so t=15//
(b)sub t=15 into (1)
S1=150m//
c)by v=u+at
v1=(2)(15)=30
u2=30,t=2,a=2,S3=?
S3=(30(2)+(0.5)(2)(2^2)
S3=64m
2008-04-03 21:48:24 補充：
c)寫漏了......
distance travelled by the truck=2x10=20m
The answer is S3-20=44m//
2008-04-03 21:50:17 補充：
b)看錯了how far!
by v=u+at
v=(2)(15)=30//
參考: , 唔選我唔該通知聲
收錄日期: 2021-04-19 21:40:44
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080403000051KK02418