[問題] 平行方向的力推懸吊方塊做的功

[Marqquet (The limit is sky)]

────┬─────
        │╲
        ｜  ╲  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？

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◆ From: 163.25.97.171
→ chtm:位能增加是繩子張力造成的
推 ntust661:條件不足XD
推 Qmmmmnn:total work = work done by F, Tension and mg?
※ 編輯: Marqquet        來自: 163.25.97.171        (10/25 20:51)
※ 編輯: Marqquet        來自: 163.25.97.171        (10/25 20:52)
推 aesth:能量守恆
→ mathfeel:樓上錯了。張力方向和運動軌道垂直，所以不做功。做功的
→ mathfeel:只有推力和重力。因為你考慮重力在做功，所以不能考慮它
→ mathfeel:的位能，否則會重算。
→ chtm:我傻了