问题 选择题

某海滨浴场,水底布满鹅卵石,水中游泳的人由深水走向浅水的过程中,以下体验和分析合理的是(  )

A.脚越来越不疼,因为人越来越轻

B.脚越来越疼,因为人越来越重

C.脚越来越不疼,因为人的浮力越来越大了

D.脚越来越疼,因为人的浮力越来越小了

答案

人在水中由深水走向浅水时,由于人排开水的体积减小,故人所受浮力减小;

因人在水中受到重力、浮力及支持力三个力,因人在竖直向上处于平衡状态,故有:G=F+F;

因浮力减小,重力不变,故支持力增大,所以人的脚将越来越疼.

故选D.

阅读理解

Dukuly Dogbah, a 14-year-old Liberian(利比亚的) boy, grew up in a war. He was born in the same year the Liberian war started. Since then fighting between the government forces and the rebel armies has not stopped.

Dukuly is one of around 10,000 child soldiers in Liberia. At 10, Dukuly lost contact with his family in the war and had to fight for the rebels. During the war he learnt to kill people with guns. He has killed many people and seen many of his friends die. “You have to," he said, "because it is war."

Lots of children had to join the army. Some did it out of their own will. They thought they would be safe with a gun. The army leaders use child soldiers because they are easy to control and do not get paid much.

Child soldiers do terrible things. Most of them take drugs. “I cannot control myself because it makes me brave," Dukuly said.

There are 120,000 child soldiers in Africa and 300,000 around the world. Many child soldiers die and nobody cares for them. According to a United Nation's report, 23 armies in the world use children. Some African and Asian countries often use child soldiers. Myanmar(缅甸) has the highest number of child soldiers in their army:  around 50,000. Most of the child soldiers are under 18 years of age and the youngest is only 7 years old.

The UN has called for the protection of children in war. The UN Children's Fund wants African countries to ban(禁止) child soldiers. Many UN organizations are trying to take child soldiers away from war and send them back to school.

小题1:Dukuly was born when    .

A.the Liberian war started

B.his family were killed in the war

C.he lost touch with his family

D.the government armies caught him小题2:The following are the reasons for so many child soldiers EXCEPT_______.

A.they are easy to control

B.they don't get much paid

C.having a gun makes them feel safe

D.they like to do terrible things.小题3:There are        child soldiers all over the world.

A.120.000

B.300,000

C.420.000

D.50,000小题4:According to the last two paragraphs,we know that the UN       .

A.has calle for people to protect children in war

B.has banned African countries from having child soldiers

C.has sent those child soldiers back to school

D.has taken the child soldiers under 7 away from war

多项选择题