有一題數:
有架火車開頭accelerate, 跟住constant velocity,跟住decelerate
甘要係accelerate果個period計個friction,
(佢比左pulling force,acceleration同mass)
就計倒個friction喇,
跟住再計係constant velocity果個period既pulling force,
甘答案係同friction一樣喇因為net force = 0
好喇緊住就要計係deceleration果個period既braking force
但係個答案就係將deceleration乘個mass,
點解唔洗理個friction呢??
friction唔係同個motion of a body opposite架咩?
架火車decelerate果陣都係向前行緊,
點解唔洗加番個friction??
唔洗 F - friction = ma??
明唔明??打得好亂...sorry
PHYSICS野 : fricion
2008-09-07 8:30 pm
回答 (3)
2008-09-07 11:24 pm
✔ 最佳答案
friction唔係同個motion of a body opposite架咩?架火車decelerate果陣都係向前行緊,
點解唔洗加番個friction??
唔洗 F - friction = ma??
You are asked to find the 'braking force'.
The braking force is just the force to stop the train which is provided by friction.
At the stage of motion (decceleration), the only force acting on the train is friction, thus you have the equation : friction = mass x decceleration
I think you could be aware that the value of 'friction' obtained in the decceleration period is different (normally is larger because of braking) from that in the acceleration period.
2008-09-08 3:31 am
火車accelerate, friction 向前,同呔 opposite direction
constant velocity no friction
decelerate, friction 向後,同呔 opposite direction
constant velocity no friction
decelerate, friction 向後,同呔 opposite direction
2008-09-07 9:51 pm
呢個相信係個tricky位
其實成件事入面係假設左架火車一直係[線]住黎行,個車輪根本冇轉
braking force係靠火車同路既friction,不是外力
唔同acceleration果個外力加俾佢既pulling force
所以 deceleration乘mass就係答案
其實成件事入面係假設左架火車一直係[線]住黎行,個車輪根本冇轉
braking force係靠火車同路既friction,不是外力
唔同acceleration果個外力加俾佢既pulling force
所以 deceleration乘mass就係答案
收錄日期: 2021-04-13 16:03:07
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080907000051KK00866