如下图，重力为6×l04N的汽车，在2×l03N的牵引力作用下，在平直公路上行驶，用固定于路边的照相机连续两次对其拍照，两次拍照时间间隔为2s，车长为16 m．
(1)汽车的速度有多大？
(2)汽车重力做的功是多少？牵引力做的功是多少？
(3)据以上探究过程，你能总结出计算做功时应注意什么问题？
解：(1)从图中看出：在t=2 s内，汽车向左移动的距离为一个车身长，
即s =16 m，
故v=s/t =16 m/2 s =8 m/s．
(2)汽车的重力竖直向下，在此方向上汽车没有移动距离，所以WG =0．
汽车的牵引力F =2×103N，在此方向上移动的距离s=16 m．
所以WF =Fs =2×103N×16m =3.2×104J.
(3)据以上探究过程，我们应注意求功时，要用力和在力的方向上通过的距离的乘积求功，如果在某个力的方向上无距离，则该力做的功等于零．
| 完形填空。 | |||
| A little boy invited his mother to attend his school's first parent meeting. To the little boy's 1 , she said she would go. This would be the first time that his classmates and teacher 2 his mother. And he felt 3 for her look. Although she was a beautiful woman, there was a serious scar (疤痕) that 4 nearly all the right side of her face. The boy never wanted to 5 why or how she got the scar. At the meeting, the people were 6 by the kindness and natural beauty of his mother although there was the scar on her face. But the little boy was still unhappy and 7 himself from everyone. However, he could 8 the conversation between his mother and his teacher. The teacher asked 9 , "How did you get the scar on your face?" The mother replied, "When my son was a baby, he was in a room that 10 fire. I tried my best to take him to safety, but I was hurt in the face. All the people were moved, especially the boy. | |||
|