→ ntust661:一開始嘗試用C.V.來解，但是流力都忘光了 囧 07/30 22:12
推 PTTers:這就回到dW = F ds 跟 W=dE/dt 那個更基本了. 07/30 22:21
→ PTTers:看來應該是我錯了.dW = F ds好像更基本 ? 07/30 22:23
推 PTTers:但 dm v^2 這一項實在太奇怪了. 它到底是什麼 ? 07/30 22:29
→ PTTers:如果題目改為 dm ,dv 都不為0.我們依然可以找到mvdv是動能. 07/30 22:31
→ PTTers:但 dm v^2 到底又是什麼 ? 07/30 22:32
→ chungweitw:dw = F ds is the definition of work. 07/30 22:38
→ chungweitw:Why are you so confused? It has nothing to do with 07/30 22:38
→ chungweitw:mass.. 07/30 22:38
→ chungweitw:Power of work P = dW/dt = F v. 07/30 22:38
→ chungweitw:work is different from (kinetic) energy. 07/30 22:39
→ chungweitw:P = d(mv^/2) / dt is correct when m is constant.. 07/30 22:42
→ chungweitw:This is the work-energy theorem... 07/30 22:42
→ chungweitw:It's not the definition of power of work. 07/30 22:42
推 PTTers:我贊成 "work is different from kinetic energy" 07/30 22:52
→ PTTers:但如果work跟 totol energy 的改變無關的話也太怪了. 07/30 22:53
→ PTTers:而且之前不是推出了 P = Fv + ∫d(v^2)/dt dm ? 07/30 22:53
→ PTTers:P = FV 不一定成立吧 >_< 07/30 22:53
→ chungweitw:P = dW/dt = Fds/dt = Fv. No any flaw.. 07/30 22:54
→ chungweitw:work should be the same as change of total energy 07/30 22:55
→ chungweitw:Here, more and more mass gets energy. 07/30 22:55
推 Ertkkpoo:但c大的那個式子p=Fv我覺得就那行推導，是定質量才能用 07/31 12:02
→ Ertkkpoo:因為如果F=μv^2，那F=F(t)，在推導時，寫成F(ds/dt) 07/31 12:03
→ Ertkkpoo:似乎就把F視為和t無關? 至於結果會對，不知道是不是碰巧? 07/31 12:05
→ Arry2000:在這題中，μ和v都是定值，所以F不是t的函數才會P=Fv 07/31 12:25
→ chungweitw:No. 07/31 12:30
→ chungweitw:P = Fv...That's it. 07/31 12:30
→ chungweitw:It has nothing to do with mass; it doesn't matter 07/31 12:31
→ chungweitw:whether F depends on t. 07/31 12:31
推 Ertkkpoo:了解 07/31 14:32