问题 问答题

如图所示,右端有固定挡板的滑块B放在光滑的水平面上.B的质量为M=0.8kg,右端离墙壁的距离L=0.09m.在B 上靠近挡板处放一质量m=0.2kg的小金属块AA与挡板之间有少量炸药.AB之间的动摩擦因数μ=0.2.点燃炸药,瞬间释放出化学能.设有E0=0.5J的能量转化为AB的动能.当B向右运动与墙壁发生碰撞后,立即以碰撞前的速率向左运动.A始终未滑离Bg=10m/s2.求:

(1)AB刚开始运动时的速度vAvB

(2)最终AB上滑行的距离s

答案

(1)vA=2m/s,方向向左;vB=-0.5m/s,方向向右.(2)0.74m

(1)AB在炸药点燃前后动量守恒.取向左为正方向,则

解得vA=2m/s,方向向左;vB=-0.5m/s,方向向右

(2)B运动到挡板处时,设AB的速度分别为,取向左为正方向,由动量守恒定律可得

B,由动能定理可得

解得=1.6m/s;=-0.4m/s,方向向右

AB最终保持相对静止时的共同速度为v

由动量守恒定律,有

由能量守恒定律,有

解得s=0.74m

阅读理解

阅读理解。

     Growing up in Philadelphia, Lieberman started cooking with his stay-at-home dad when he was seven.

His food-loving family had two kitchens, and he quickly learned what was the best way to bake his cakes.

Lieberman improved his kitchen skills greatly during a year abroad before college, learning from a cook in

Italy and studying local specialties (地方特色菜) in Germany, Spain and France. At Yale, he was known

for throwing dinner parties, single-handedly frying and baking while mixing drinks for dozens of friends.

Just for fun, he and some friends decided to tape a show named Campus Cuisine about his cooking.

Lieberman was a real college student showing his classmates how to do things like make drinks out of dining-

hall fruit. That helped the show become very popular among the students. They would stop Lieberman after

classes to ask for his advice on cooking. Tapes of the show were passed around, with which his name went

beyond the school and finally to the Food Network.

     Food Network producer Flay hopes the young cook will find a place on the network television. He says

Lieberman's charisma is key. "Food TV isn't about food anymore," says Flay. "It's about your personality

(个性) and finding a way to keep people's eyeballs on your show."

     But Lieberman isn't putting all his eggs in one basket. After taping the first season of the new how,

Lieberman was back in his won small kitchen preparing sandwiches. An airline company (航空公司) was

looking for some one to come up with a tasteful, inexpensive and easy-to-make menu to serve on its flights,

Lieberman got the job.

1. We can learn from the text that Lieberman's family _____.

A. have relatives in Europe

B. love cooking at home

C. often hold parties

D. own a restaurant

2. The Food Network got to know Lieberman _____.

A. at one of his parties

B. from his teachers

C. through his taped show

D. on a television program

3. What does the word "charisma" underlined in the text refer to?

A. A natural ability to attract others.

B. A way to show one's achievement.

C. Lieberman's after-class interest.

D. Lieberman's fine cooking skill.

4. Why did the airline company give Lieberman the job?

A. He could prepare meals in a small kitchen.

B. He was famous for his shows on Food TV.

C. He was good at using eggs to make sandwiches.

D. He could cook cheap, delicious and simple meals.

5. What can we learn about Lieberman from the text?

A. He is clever but lonely.

B. he is friendly and active.

C. He enjoys traveling around.

D. He often changes his menus.

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