问题 选择题

如图所示,物体A B C放在光滑水平面上用细线a b连接,力F作用在A上,使三物体在水平面上运动,若在B上放一小物体D,D随B一起运动,且原来的拉力F保持不变,那么加上物体D后两绳中拉力的变化是(   )

A.Ta增大

B.Tb增大

C.Ta变小

D.Tb不变

答案

答案:A

以整体为研究对象,质量增大加速度减小,以C为研究对象,绳子b提供加速度,所以绳子b的拉力减小,再以A为研究对象F-Fa=ma,可知绳子a的拉力增大,A对;

阅读理解

Long ago there was a man with the name Smith. He made a living by making caps. One day he went to sell his caps. He went through a forest. There were many monkeys in it. It was very hot. The man is very tired and wanted to have a rest. He came up to a large tree, put his caps on the ground, took one of them and put it on his head. Then he lay down and soon fell asleep.

  “Where are my caps?” Smith cried when he woke up.He looked up and saw many monkeys in the tree and each monkey had a cap on its head.

  “Give me back my caps!” the man shouted at the monkeys.But the monkeys didn't understand him.They only laughed.The man got angry,took off his own cap,threw it on the ground and cried,“If you want all my caps,you may take this one,too!”

  And what do you think happened?The little animals did the same. Each monkey took off its cap and threw it on the ground. The man was very glad. He quickly collected all his caps and went on his way.

小题1:The cap­maker was so tired ______.

A.that he wanted some food

B.that he wanted to sell his caps in the forest

C.that he had to stop for a rest

D.that he wanted to return home小题2:He ______ and lay down and fell asleep soon.

A.put all his caps on his head

B.put all his caps on the ground

C.put all his caps in the tree

D.put one of his caps on his head小题3:When the man woke up,he found ______.

A.each monkey had a cap on its head   

B.some monkeys were stealing his caps

C.the monkeys were laughing at him  

D.a monkey had stolen his cap and tried it on小题4:The man cried and told the monkeys ______.

A.to return his caps   

B.not to get away with his caps

C.to buy his caps   

D.not to laugh at him小题5:At last the monkeys threw the caps on the ground because ______.

A.they took pity on him   

B.the man had got angry

C.they didn't like the caps

D.they liked to do the same as the man did

单项选择题