问题 计算题

如图所示,将一块重为3N,体积为100cm3的石块,用细线系着浸没在装有水的圆柱形容器中,容器中水的深度由10cm上升到12cm. (容器的重力和容器壁的厚度忽略不计,g=10N/kg). 求:(12分)

(1)石块所受浮力;

(2)容器中水的重力;

(3)细线松动,石块沉到容器底静止后,容器对水平地面的压强.

答案

解:(1)F=pvg=1.0×103kg/m3×10-4m3×10N/kg=1N

(2)V=10cm/(12cm-10cm)×100cm3=500cm3

G=pvg=1.0×103kg/m3×5×10-4m3×10N/kg=5N

(3)P=F/S=(G+G)/(V/h)=(5N+3N)/5×10-3m2=1.6×103P

(1)石块所受浮力FgV=1×103kg/m3×10N/kg×100×10-6m3=1N.

答:石块所受浮力为1N.

(2)容器底面积S=

水的体积V=Sh=50cm2×10cm=5×102cm3

水的重力G=mg=ρgV=1×103kg/m3×10N/kg×5×102×10-6m3=5N.

答:容器中水的重力为5N.

(3)容器对水平地面压强为P= P=F/S=(G+G)/(V/h)=(5N+3N)/5×10-3m2=1.6×103P

答:容器对水平地面的压强为1.6×103Pa.

阅读理解

阅读理解。

     There are some easy things you can do to protect the environment and the earth .Choose ideas from

the list or come up with a few of your own.

Plant flowers ,grass or trees .

     Whenever you visit a park or  a beach ,take away what you bring there —keep rubbish in a bag until  

you can put it in a dustbin.

Turn off the lights ,Tv  sets when you leave the room .This saves a  lot of electricity.

     Turn off the tap(水龙头) when you brush your teeth. You can save some water by not letting it run .

Also,use a glass cup instead of a paper cup ,because this saves paper.

     Keep the doors and windows closed in winter to keep warm air in .

     Give your old books and magazines to library instead of throwing them away.

     Give your okd clothes to poor children you know instead of throwing them away.

     Use both sides of paper.

     Stop pouring dirty water into the rivers or lakes nearby.

     Encourage all your friends to do the same things you do to help protect the earth.

     You don’thave to wait until Earth Day to do these  things.Make every day Earth Day .

     If everyone make’s a contribution to protecting the environment ,the world will become much more

beautiful.

1.From the above,we know that this is _______

A.a  sign  

B.a proposal(倡议书)

C.an advertisement

D.a notice

2.The writer tells us_______.

A.to throw rubbish into a dustbin

B.to pour dirty water into the rivers

C.to save water by letting it run while we are brushing our teeth

D.that we cn’t do all these things until Earth Day

3.We can _______to save paper.

A.use a paper cup

B.use both sides of paper

C.give lkd books to a library

D.pick up waste paper at a school

4.Which of the following is wrong according to the writer?

A.Turn off the lights when you leave the room.

B .Close the doors in winter.

C. Use a paper cup when you brush your teeth.

D.Gve your old clothes to the poor children.

5.The main idea of this passage is how to _______

A.save money

B. save water and electricity

C. make better use of old things

D.protect the earth

单项选择题