更新1:
我想問呢 點解downward journey o個時 冇mgsin theta 但係上去先至有既?? 解答埋我依題就可以拿最佳解答的了!
Physics: Power
2008-06-10 2:40 am
A bicyclist coasts down a 7.0 degree hill at steady speed of 5.0m/s. Assuming a total mass of 75kg (bicycle plus rider), what must be the cyclist's power output to climb the same hill at the same speed?
回答 (2)
2008-06-10 2:57 am
✔ 最佳答案
The Q is solved as follows:圖片參考：http://i238.photobucket.com/albums/ff245/chocolate328154/Phy035.jpg?t=1213009052
2008-06-09 19:36:25 補充：
I have added in some more explanation, plx press reload to view it.
2008-06-10 13:13:46 補充：
mgsin theta就係個weight component down the slope嚟嘅, 上去同落去都有。
2008-06-10 13:20:05 補充：
已經再改咗圖解釋, 再有問題歡迎提出。
參考: My Phy Knowledge
2008-06-10 3:10 am
我都唔知岩唔岩= =
先睇down the slope,
畫個力圖出黎, 見到有Wsin7 and f(friction)兩個相反方向horizontal force,
因為constant speed, so net force = 0
Wsin7 - f = 0
f = 750sin7
再睇up the slope,
畫個力圖出黎, 見到有兩個向下horizontal force(同上slope唔同!), Wsin7, f
要向上ride constant speed 5m/s, 即要against果兩個force.
因net force = 0,
我地可以use 呢條formula, P = Fv
power output by bicyclist = (force given by rider to against the 2forces)(5m/s)
= (Wsin7+f)(5)
= (750sin7x2)(5)
= 914W
先睇down the slope,
畫個力圖出黎, 見到有Wsin7 and f(friction)兩個相反方向horizontal force,
因為constant speed, so net force = 0
Wsin7 - f = 0
f = 750sin7
再睇up the slope,
畫個力圖出黎, 見到有兩個向下horizontal force(同上slope唔同!), Wsin7, f
要向上ride constant speed 5m/s, 即要against果兩個force.
因net force = 0,
我地可以use 呢條formula, P = Fv
power output by bicyclist = (force given by rider to against the 2forces)(5m/s)
= (Wsin7+f)(5)
= (750sin7x2)(5)
= 914W
參考: myself
收錄日期: 2021-04-19 01:25:00
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080609000051KK02349