问题 选择题

关于自由落体运动,以下说法不正确的是(  )

A.下落过程中加速度一定不变

B.第1s末与第2s末的速度比为1:2

C.下落位移与下落时间的平方成正比

D.下落过程中,物体处于平衡状态

答案

A、自由落体运动只受重力,故加速度恒等于重力加速度,即加速度不变,故A正确;

B、根据v=gt可知在开始连续的两个1s末的速度大小比是1:2,故B正确;

C、根据h=

1
2
gt2,下落位移与下落时间的平方成正比,故C正确;

D、下落过程,物体只受重力,故不平衡,故D错误;

本题选错误的,故选D.

单项选择题

Letter A

Dear Rose,

I like your programmes very much. I’m now writing to ask you something about American social customs. My American friends want me to join them in their dinner party. I am very happy and have decided to go, but I’m a little worried about it, too. The social customs in my country are very different from here, so I’m afraid of making mistakes.

Should I bring a present, such as sweets or flowers Should I arrive on time or a little late At the dinner table, how can I know which fork or knife to use How can I let the family know that I’m thankful for their kindness

Wang Lin

Letter B

Dear Wang Lin,

It’s a good idea to bring a small present when you go to a dinner party. Flowers are always nice, or you may bring a bottle of wine if you know that your friends drink it.

You should arrive on time or five to ten minutes late. Don’t get there early. If you’re going to be more than fifteen minutes late, you should call and tell them.

Try to be free at the dinner table. If you don’t know about choosing the right fork or knife, just watch the other people, and follow them. If you still have no idea of what to do, ask the person next to you.

If you like the food, say so. Of course, you’ll thank them for the meal and for their kindness. It’s also a good idea to send a thank you card the day after.

Rose

If you’re asked to a dinner party but not sure about what to bring as a present, it’s good to bring().

A.some fruits

B.a bottle of wine

C.some flowers

D.a knife and fork

名词解释