匀速运动时 Fcos37=f = 8N N=mg-Fsin37 =20-6=14N 动摩擦系数u=6/14=3/7 当 F'=30N时 N'=mg-F'sin37 =20-18=2N f'=uN'=3/7*2=6/7N ma=F'cos37-f'2a=30*0.8-6/7a= 11.43m/s^2
