[力學] 96中山 功與能
[單元]
功與能
[來源]
96 中山 (9)
[題目]
As a block slides a distance d down an incline, the incline
exerts a constant frictional force of magnitude f on the block.
The quantify fd gives the magnitude of:
(A) The work done by the frictional force
(B) The change in the internal energy of the block
(C) The change in the internal energy of the block-incline system
(D) The change in the mechanical energy of the block-earth system
(E) The change in the kinetic energy of the block
[想法]
手邊一個答案是說無解, 另外一個答案給(C)
前者的話, 我的想法是題目給的 fd 相乘為正值
然而不論是根據定力作功 W = F dot d,
或是根據功能原理 W_nc = (K2 + U2) - (K1 + U1)
其作功值, 總力學能變化值皆為負, 故不合。
然而後者若是不考慮正負, 只考慮其量值,
是否(A)也可以選?
考慮定力作功, W = -fd, 則 |-fd| = fd
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 114.46.140.235
推
05/20 20:43, , 1F
05/20 20:43, 1F
→
05/20 20:44, , 2F
05/20 20:44, 2F
題目並沒有明確地指明斜面是否固定, 或是本身唯一有質量之楔形,
應該僅是指一斜面, 且表明下滑, 定摩擦力與其位移方向相反,
作負功。
至於ｍ大說的內能變化我不太明白, 內能應該是指微觀狀態下,
物塊內部各粒子的動能與位能和, 此題要看的應該是有無熱能散失?
※ 編輯: EggAche 來自: 114.46.140.235 (05/20 20:54)
推
05/21 10:28, , 3F
05/21 10:28, 3F
→
05/21 10:30, , 4F
05/21 10:30, 4F
→
05/21 10:30, , 5F
05/21 10:30, 5F
→
05/21 10:34, , 6F
05/21 10:34, 6F
→
05/21 11:46, , 7F
05/21 11:46, 7F
→
05/21 11:46, , 8F
05/21 11:46, 8F
→
05/21 16:38, , 9F
05/21 16:38, 9F
→
05/21 16:38, , 10F
05/21 16:38, 10F
→
05/21 17:49, , 11F
05/21 17:49, 11F
→
05/21 17:50, , 12F
05/21 17:50, 12F
推
05/21 17:51, , 13F
05/21 17:51, 13F
推
05/21 22:33, , 14F
05/21 22:33, 14F