推 ntust661:讚 10/25 21:15
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※ 引述《Marqquet (The limit is sky)》之銘言：
: ────┬─────
: │╲
: ｜ ╲ L
: ｜ ╲
: L∣ ╲
: ｜ ╲
: ｜ F→■
: ｜
: F→■
: ←— d —→
: 完整題為：
: A 230kg brate hangs from the end of a rope of length L = 12.0m.
: You push horizontally on the crate with a varying force F to move it
: distance d = 4m to the side.
: (a) What is th magnitude of F when the crate is in this final position.
: During the displacement,what are
: (b) the total work done on it.
: (c) the work done by the gravitational force on the crate.
: (d) the work done by the pull on crate from the rope.
: (e) Knowing that the crate is motionless before and after its displacement,
: use the answers to (b)(c)(d), to find the work your force F does on the
: crate.
: 為什麼(b)答案是 0 ？
: F 即使沒有使動能改變，應該有貢獻位能的部分才對？
功能定理
合力做功=動能變化
已知繩張力不做功
只有F和重力做功
假設整個推動過程狀態為quasi-equilibrium
動能變化=0
故合力做功=0 #
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