如图所示，x-t图象和v-t图象中的四条图线1、2、3、4分别表示四个不同物体的运动情况，关于它们的物理意义，下列判断正确的是 
A．图线1表示物体做曲线运动
B．x-t图象中的t1时刻v1＞v2
C．v-t图象中0至t3时间内4的平均速度小于3的平均速度
D．两图象中的t2、t4时刻分别表示两物体开始反向运动
答案：B
题目分析：图线1的斜率始终大于零，说明物体的速度始终大于零，表示物体一直沿正方向运动，说明物体做直线运动．故A错误．x-t图象中
时刻图线1的斜率大于图线2的斜率，则有
．故B正确．
v-t图象中0至t3时间内图线4的“面积”大于图线3的“面积”，则4的位移大于3的位移，所用时间相等，则4的平均速度大于3的平均速度．故C错误；．x-t图象中
时刻表示2的速度反向，而图线4的速度一直为正，说明速度方向没有反向．故D错误．
故选B
点评：本题中X-t图象与v-t图象形状相同，但物理意义不同，关键根据斜率的物理意义分析物体的运动情况．
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| It is a thousand kilometers across that desert (沙漠). The road is 1 nearly all the way. Sometimes there is a deep sand. A driver must then put his foot down hard and drive through! There are three small 2 along the way. Vick reached the first place at ten o'clock p. m. He had his 3 in a little restaurant (餐馆) there. It was a warm 4 in August. Vick wanted to 5 through the night. The nights are warm enough in August, but the days are very, very 6 . He left the restaurant at 11: 30 and drove over 7 hours. There wasn't a moon, but the 8 were wonderful. There was nothing else on die road. Vick thought, "It's an empty desert. No tree, house, man. "He could 9 . the endless, white road in the car's headlights (车灯). A million stars looked down on him. It was two o'clock in the morning. Vick stopped the car. He was two hundred kilometers from the 10 town: "I'll light the cooker (炊具)," he thought, "and make some tea. " He got out of the car. He heard some sounds, ten or fifteen metres 11 . He could not see anything in the darkness (黑暗). A man said, "Good morning. It's a 12 morning, isn't it?" The man came forward (向前), out of the darkness; out of the desert. Vick did not move. The man said, "You are going to 13 some tea, aren't you? I often get a cup of tea at this time. It" s two o'clock. Cars always 14 near here at this time. Sometimes I get a 15 . Now listen, and I'll tell you a story. Then you'll give me..." |
| ( )1. A. short ( )2. A. cities ( )3. A. tea ( )4. A. night ( )5. A. live ( )6. A. cold ( )7. A. two ( )8. A. trees ( )9. A. see ( )10. A. home ( )11. A. about ( )12. A. noisy ( ) 13. A. eat ( )14. A. leave ( )15. A. bread | B. good B. hotels B. supper B. day B. stay B. cool B. seven B. animals B. ride B. other B. from B. lovely B. make B. stop B. car | C. busy C. villages C. lunch C. season C. drive C. hot C. ten C. stars C. pass C. next C. far C. sleepy C. cook C. meet C. rest | D. well D. towns D. breakfast D. month D. walk D. warm D. fourteen D. clouds D. find D. last D. away D. sunny D. drink D. run D. meal |