问题 问答题

子弹用2×10-4s的时间穿过一固定木板,穿入木板的速度是800m/s,穿出木板的速度是300m/s,子弹在木板中运动的加速度恒定.

(1)子弹穿过木板时加速度是多大?

(2)木板的厚度是多少?

(3)如子弹打入一块同样质地的厚木板(子弹在木板中运动的加速度与第一次相同),穿入木板的速度仍是800m/s,子弹能打入多深?

答案

规定初速度方向为正方向

(1)由加速度公式得:a=

v-v0
t
=
300-800
2×10-4
m/s2=-2.5×106m/s2

故加速度大小为2.5×106m/s2

(2)由v2

-v20
=2ax

∴x=

v2
-v20
2a
=
3002-8002
2×(-2.5×106)
m=0.11m

(3)由

v21
-v20
=2
ax 1
得:

x1=

v21
-v20
2a
=
0-8002
2×(-2.5×106)
m=0.128m

答:(1)加速度大小为2.5×106m/s2

(2)木板的厚度是0.11m

(3)子弹能打入0.128m

阅读理解

Jean is a young girl who comes from a rich and famous family. She goes to a good university and has almost everything that money can buy. The problem is that Jean’s family are so busy that they can hardly find time to be with her. Jean is quite lonely (孤独的). So she spends a lot of time on her QQ. She likes being anonymous (匿名的), talking to people who do not know about her famous family and her rich life. She uses the name Linda on QQ and has made a lot of friends.

Last year Jean made a very special friend on QQ. His name was David and he lived in San Francisco. David was full of stories and jokes. He and Jean had the same interest in rock music and modern dance. So it always took them hours to talk happily on QQ and sometimes they even forgot their time. Of course, they wanted to know more about each other. David sent a picture of himself. He was a tall, good-looking young man with big, happy smile. As time went by, they became good friends and often sent cards and small things to each other.

When Jean’s father told her that he was going on a business trip to San Francisco, she asked him to let her go with him. She wanted to give David a surprise for his birthday. She would take him the latest DVD of a rock singer. But when she knocked on David’s door in San Francisco, she found that her special friend was a 70–year-old man named Jim! How disappointed Jean was!

小题1: Jean spends a lot of her time on QQ because she is_______.

A.rich

B.young

C.a bad student

D.lonely小题2:Jean thought “David” was special because he ________.

A.made her very happy on QQ

B.was from San Francisco

C.was tall and good-looking

D.was rich小题3:What are both Jean and “David” interested in? 

A.Pop music and sports.

B.Music and science.

C.Rock music and modern dance.

D.Stories and jokes.小题4:Which of the following is True?

A.Jean has got everything in her life.

B.“David” and Jean sent cards to each other.

C.“David” didn’t tell Jean his real address.

D.Jean’s family members often get together.小题5:What’s the main idea of the passage? 

A.Don’t go to meet those you get to know on QQ.

B.People don’t use their real names on QQ so often.

C.Don’t believe those you get to know on QQ easily.

D.Don’t spend much time on QQ.

问答题 简答题