[問題] 物理機械能與摩擦力

看板Physics作者cvsi04236 (ＢＢ小Ｂ)時間15年前 (2010/12/08 17:02)推噓2(2推 0噓 19→)

留言21則, 4人參與討論串1/1

[領域] 能量 [來源] Physics 5th edition vol 1 by Resnick.Halliday,Karne [題目] A solid cylinder of mass M and radius R strats from rest and rolling without slipping down an inclined plane of heigth h . Find its final speed when it reach the bottom of the plane. [解答]For the system we take the Earth and cylinder. "Even if there is a frictional present, it does not do work and so it cannot change the mechanic energy. " E前=Mgh E後= 1/2(M)(Vcm)^2 + 1/2 (Icm) (vcm/R)^2 [瓶頸] 我的問題是有關題目與解答 (1) 題目說圓柱rolling down without slipping那怎麼會有摩擦力呢? 但如果沒有摩擦力就不會轉動啦所以我覺得是題目是說過了一段時間之後圓柱用純滾動落下請問是不是這樣呢? (2) 解答的 "Even if there is a frictional present, it does not do work and so it cannot change the mechanic energy." 讓我疑惑，明明就有摩擦力系統選擇的地球與圓柱怎麼不會改變機械能呢但是答案帶進去又對了請問一下如何解釋上面那句話 (3) 請問f*s(斜面上的位移) 在這題是否為動能中的 1/2Iw^2呢? 請板上高手回答一下感激! -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 140.116.102.39

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