查看完整版本 : Energy同電學各一題

zale_lee 2012-11-13 03:30 PM

Energy同電學各一題

A cylinder rolls freely down a slope of 1 in 40. What will be its velocity after rolling 20
m from rest down the slope? If the mass of the cylinder is 50 kg, what is then its total
kinetic energy? [Given: I of a cylinder = 1/2 mr2] (ans:2.56 m/s, 245 J)


[img]http://upload.lsforum.net/users/public/l22449d%20001c132.jpg[/img]

呢兩題有冇人識計?

↗亢龍無悔↙ 2012-11-13 06:01 PM

我只係識做rotational motion
Since the word "slipping" is missing in this question, frictional force should also be considered.
m g sinθ - f = ma
τ = I α, where a = r α
Doing some simplification, a can be found.
Apply equation of motion, v can be found.
Total energy = 1/2 m v*2 + 1/2 I ω*2, where v = r ω
total energy can be found.
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