– John and I will celebrate our fortieth wedding anniversary next month.– ___________! A.Cheer up B. Well done C. Go ahead D. Congratulations 答案:D
一质量m=1kg的物体在水平恒力F作用下沿水平面运动, 1s末撤去恒力F,其v - t图象如右图所示。则恒力F和物体所受阻力f的大小是( ) A. F=8N B. F=9N C. f=2N D. f =3N