思考①其它解法？ ②在x=0~3m过程中，力的冲量？
[思考]①其它解法？ ②在x=0~3m过程中，力的冲量？
§4.2保守力(Conservative Force) 1.几种力的功 (1Work done by elastic force ◆ 0 xa Xb xa→Xb： A=F,dx=-kxd=k depends upon x and xp
§4.2 保守力 (Conservative Force) 1.几种力的功 (1)Work done by elastic force O xa xb X = L A Fx dx = − b a x x kxdx 2 2 2 1 2 1 a b = k x − k x xa→xb： ——depends upon xa and xb
2)Work done by gravity Y ha-→lhb: 4=F,山=-mg=mgh,-mgh, depends upon h and hp
(2)Work done by gravity O X Y ha hb = L A Fy dy = − b a h h mgdy = mgha −mghb ha→hb： ——depends upon ha and hb
(3)Work done by gravitational force GMm H=近=一 r.dr
(3)Work done by gravitational force dA F dr = r dr a r b r m M r dr r GMm = − 3