问题 选择题

伽利略在研究自由落体运动时,做了如下的实验:他让一个铜球从阻力很小(可忽略不计)的斜面上由静止开始滚下,并且做了上百次.假设某次试验伽利略是这样做的:在斜面上任取三个位置A、B、C,让小球分别由A、B、C滚下,如图所示.设A、B、C与斜面底端的距离分别为x1、x2、x3,小球由A、B、C运动到斜面底端的时间分别为t1、t2、t3,小球由A、B、C运动到斜面底端时的速度分别为v1、v2、v3,则下列关系式中正确,并且是伽利略用来证明小球沿光滑斜面向下的运动是匀变速直线运动的是(  )

A.

v1
2
=
v2
2
=
v3
2

B.

v1
t1
=
v2
t2
=
v3
t3

C.x1-x2=x2-x3

D.

x1
t12=
x2
t22
=
x3
t32

答案

A、小球在斜面上三次运动的位移不同,末速度一定不同,故A错误;

B、由v=at可得,a=

v
t
,三次下落中的加速度相同,故公式正确,但是不是当是伽利略用来证用匀变速直线运动的结论;故B错误;

C、由图可知及运动学规律可知,x1-x2>x2-x3,故C错误;

D、由运动学公式可知,X=

1
2
at2.故a=2
x
t2
,故三次下落中位移与时间平方向的比值一定为定值,伽利略正是用这一规律说明小球沿光滑斜面下滑为匀变速直线运动,故D正确;

故选D.

阅读理解

Like most cultures around the world, the Zulu people of Africa tell stories that have animals as heroes. These stories are meant to have fun, but they are also used to teach important lessons to children. This is one of those stories.

One hot afternoon, Jackal was walking along the rocky road sniffing (嗅) the ground. He was hoping to smell a mouse or a lizard (蜥蜴), or something else that would be good to eat. He was so much lost in sniffing that he wasn’t really paying attention to what was around himself.

Suddenly, Jackal looked up to see his neighbor, Lion, walking straight toward him. He did not have enough time to run way. Jackal had played many tricks on Lion over the years, so he knew he would be in trouble if he was caught. Jackal needed to think of something quickly.

“Help! Help!” cried Jackal as he quickly jumped upon a large rock hanging over the road. “The rocks are falling down, and I can’t hold them much longer. We shall both be crushed (压碎) if you do not do your best to hold these rocks back, Lion”

At once, Lion pushed his strong shoulder against the rocks to keep them from moving any further. “I’ll just run over here to get something to stop the rocks.” shouted Jackal as he ran way to safety. Lion stayed leaning against the unmoving rocks for quite a long time before he realized that Jackal had tricked him yet again!

小题1: Why was Jackal sniffing the ground?

A.To play with Lion.

B.To push a rock

C.To run after a mouse

D.To look for something to eat.小题2:What does the underlined word ‘leaning’ mean?

A.supporting

B.sleeping

C.running

D.sitting小题3: Why did Jackal cry for help?

A.Because Lion was rushing to him.

B.Because he was caught under a rock.

C.Because he got an idea to get away from Lion.

D.Because he saw a large rock moving toward him.小题4: What lesson does the story teach us?

A.Trust(信任) your friend, trust yourself

B.Work hard, and you’ll succeed.

C.Help others when they are in trouble.

D.Try to find a quick way out when in trouble.小题5:Which words can describe Jackal’s characteristics?

A.selfish and stubborn

B.silly and unkind

C.clever and creative

D.impolite and dishonest

单项选择题