1、3 牛顿第二定律 a m 1 _ _ 2 a F _ k F _ _ _ Fm kma 1 F kma k F m a 2 k 1 1 kg 1 m/s2 1(N)1 N _ _ 1 kg m/s2 F ma (1)()(2)()(3)()(4)()(5)F kma k 1()(6)N/kg m/s2()F ma F m a 0 0 0 ()()A B C D A D A B C D ()F ma()A m F a B F m a C F ma F a D a F m C D A B C a Fm D 1 1 2(1)(2)(3)1()F()A.B C D B C a F kxm F F a
2、kx Fm B C 2 1 a F ma 2.:(1)(2),(3)(4)3.:(1):,2 x y Fx Fy ax ay x y xxyyF maF ma 2 m 20 kg 53 F 100 N 0.2 g 10 m/s2,1 2 3 sin53 0.8 cos53 0.6,1 2 Fsin53 FN mg FN mg Fsin53 120 N 3 Ff FN 24 N Fcos53 Ff ma a 1.8 m/s2 1 2 120 N 3 1.8 m/s2 1 2 x M F A.FM B FcosM C.F MgM D Fcos Mg FsinM（）D F Mg F sin F F
3、Mg F sin F co s Mg F sin Ma a Fcos Mg FsinM（）D ()A B,MA MB,A B,F A B,a F A B,()A.A B C.MAMB B C M,:F-Mg=Ma:a=FM-g,a F,MA B,A D,B C ,:(1)?(2)?(1)(2),:,:(1)?(2)?(1),(2):1.()(T4)2 kg,120,14 N,()A.14 2 N B.7 2 m/s2 C.14 N D.7 m/s2 C D 120,14 N,a=Fm,a=7 m/s2,C D 2.()F=kma k,()A.1 B.k C.k D.1 N 1 kg 1 m/s2 C D F=kma,m a F,k 1,C,A B;m a F,k=1,1 N=1 kg m/s2,1 N 1 kg 1 m/s2,D 3.,a,F F a()C,F-Ff=ma,F=ma+Ff,a=0,F=Ff;F=0 a=-fFm C 4.(2021)10 g,300 m/s,200 m/s 10 cm,x=10 cm=0.1 m,m=10 g=10-2 kg,a=2vv2x=22200 3002 0.1 m/s2=-2.5 105 m/s2,F=ma=10-2(-2.5 105)N=-2.5 103 N,:2.5 103 N,
