问题 选择题

质量均为m的两个物体,A放在光滑水平面上,B放在粗糙水平面上,在相同水平推力F作用下,两物体移动了相同的位移s,下列说法正确的是

A.在粗糙水平面上所做的功多

B.两次所做的功一样多

C.两次F的平均功率一样

D.在粗糙水平面上平均功率大

答案

答案:B

由功的公式W=Fs,可知A错;B对;但由于两次运动加速度不同,运动时间不同,力F的平均功率不同,在粗糙水平面上的运动时间较长,平均功率较小,D错;

阅读理解

Ironing a shirt is easy to learn. Just follow the steps in this short guide (指南), and you’ll learn how to iron your shirt properly with the help of the video. The most important thing is this: don’t try to iron a dry shirt.

● Get ready

You will need an iron, an ironing board and a bottle of water. Place the shirt on the ironing board. You can iron in whatever order you like, but most people like to start at the top — the collar. Have a bottle of water ready. Spray (喷) it onto the shirt to make it easier to iron.

● Do the ironing

First, iron the inside of the collar. Second, turn the collar over and iron the other side. Third, iron the back shoulders of the shirt. Fourth, iron the cuffs. Iron the inside, then the outside of the cuffs. Fifth, iron the sleeves. Sixth, iron the back of the shirt. Finally, iron the front of the shirt. Do one side, and then do the other side.

● Dry the shirt

Check your shirt and iron it again if you need to. Now put your shirt on a hanger and let it dry.

小题1: What’s the most important thing if you want to iron a shirt?

A.Have a bottle of water ready.

B.Don’t try to iron a dry shirt.

C.Wash your shirt carefully.

D.Place the shirt on the ironing board.小题2:You will need all of the following things EXCEPT ________ before you iron a shirt.

A.a ruler

B.an iron

C.an ironing board

D.a bottle of water小题3:Most people like to start with ironing ________ of a shirt.

A.the sleeves

B.the back shoulders

C.the cuffs

D.the collar小题4:How many steps are there to do the ironing, according to this guide?

A.Five.

B.Six.

C.Seven.

D.Eight.小题5:The writer tells us it’s easy to learn how to iron a shirt by ________.

A.reading a book

B.watching a video

C.listening to the radio

D.reading the newspaper

判断题