【简答题】A.They are paying for his education. B.They invited him to their party. C.They took him on a vacation with them. D.They let him live with them for free.
【简答题】如图甲所示,物体放在粗糙程度相同的水平地面上,受到方向不变的水平推力 F 的作用, F 的大小与时间 t 的关系和物体运动速度 v 与时间 t 的关系如图乙所示。由图像可知,当 t =1s时,物体处于 状态;当 t =3s时,物体受到的摩擦力力为 N;当 t =5s时,推力对物体做功的功率为 W。