1、 1 1 ( ) A B C D D 2 4 1 14 ( ) 4 1 14 A (1) F B (2) F C (3) F D (4) F D F W F scos W D 3 t 0 1 m/s. F F v 4 1 15 4 1 16 1 2 3 F W1 W2 W3 ( ) 4 1 15 4 1 16 A W1 W2 W3 B W1 W2 W3 C W1 W3 W2 D W1 W2 W3 B v t 1 2 3 x1 v0 2 t 1 2 m x2 v0 2 t 1 2 m x3 v0t 1m F1 1 N F2 3 N F3 2 N. W1 F1x1 1 2 J.W2 F2x2 3
2、2 J W3 F3x3 2 J W1W2W3. 4 398 13 15 ( ) 2 A B C D C C 4 1 17 5 4 1 17 A B F B B F W1 B F W2 ( ) A W1 W2 B W1 W2 C W1 W2 D AB 6 ( ) A ( ) B C D AD D A 4 1 18 7 2 kg F 4 1 18 10 N ( ) A 150 J B 100 J C 250 J D 250 J AD 5 s s 25 m 2 m/s 2 F F ma F F ma (10 4) N 6 N F WF Fs 150 J F W F s 250 J 3 4 1 19
3、8 4 1 20 t0 2t0 s1 s2 v1 v2 t0 W1 t0 2t0 W2 ( ) A s2 5s1 v2 3v1 B s2 9s1 v2 5v1 C s2 5s1 W2 8W1 D v2 3v1 W2 9W1 AC t0 a1 a2 a2 2a1 v1 a1t0 v2 v1 a2t0 3v1 s1 1 2 a1t 2 0 s2 s1 v1t0 1 2 a2t 2 0 5s1 W1 F0s1 W2 2F0(s2 s1) 8W1 A C B D 9 1 kg g 10 m/s 2 3 s WG _ 3 s WG _. 450 J 250 J 3 s h1 1 2 gt 2 3 1 2 2m 45 m 3 s W1 mgh1 450 J 3 s h2 1 2 gt 2 3 1 2 gt 2 2 1 2 2 2 2 ) m 25 m 3 s W2 mgh2 250 J. 4 1 20 10 4 1 20 h 30 m 0.1. m 50 kg. ( g 10 m/s 2 0.6 0.8) WG 4J WN 0 Wf 3J WG mgh 4J WN 0 Wf f l h 3J.
