问题 填空题

如图所示,质量为lkg的物体静止在倾角为30°的斜面上.①画出物体受力的示意图;②物体受到静摩擦力的大小为______;③物体受到弹力的大小为______;④物体受到的合力大小为______.

答案

①分析物体的受力情况:重力mg、斜面的支持力N和静摩擦力f,画出受力的示意图如图所示.

②、③根据平衡条件得

   N=mgcos30°=10×

3
2
N=5
3
N

   f=mgsin30°=5N

④物体静止时,根据平衡条件得知合力为0.

故答案为:

①物体受力的示意图如图所示.

②5N.

③5

3
N.

④0

阅读理解

阅读理解。

     Jess really felt very happy. When he arrived at his seat in the classroom that morning, he found an

invitation (请柬) on his desk. It was from several of his classmates asking him to join them on a camping trip.

This was the first time he was asked to join in an out-of-school activity. Why were they asking him now?

Nobody seemed to like him. In fact, he had been so lonely that he drowned his feeling with food. As a result,

he had put on a lot of weight, and this gave the kids something more to make fun of him.

     Cindy, who was standing near Jess when he read the invitation, went out quickly to tell the others that the

trick (恶作剧) had worked. Everyone was pleased that Jess thought that was true. But there was no camping

trip. The whole thing was made up.

     At first, Cindy thought it was fun. But later, when Jess told her that he was going to buy a sleeping bag

with his savings (积蓄), Cindy had a second idea. She knew that Jess's family had little money, and she hated

to see him spend his savings on something he would never use. Cindy also hated to tell Jess the truth. Her

close friends would be angry with her. What could she do now?

1. The sentence "…he drowned his feeling with food" means "______ ".

A. he ate a lot to make himself feel less lonely

B. he asked for a lot of food from his classmates

C. he brought his food to his classmates

D. he had a lot of food to put on weight

2. What would happen if Cindy told Jess the truth?

A. Jess would go on the camping trip himself.

B. Jess's family would be angry with Cindy.

C. Cindy might have trouble with her friends.

D. Jess would be thankful to his classmates.

3. If Jess really bought a sleeping bag, _______.

A. everyone else would also buy one

B. it would be the best in the class

C. Cindy would pay for it

D. He would have it for no use

4. From the story we can guess _______.

A. everybody would go camping in the class

B. Jess had few friends in the class

C. Cindy was Jess's best friend I the class

D. Jess joined in many out-of-school activities

5. Choose the best title for this passage.

A. Jess and His School

B. Jess and His Friends

C. An Invitation for Jess

D. Jess and His Camping Tip

单项选择题