问题 选择题

一质点在半径为R的圆周上从A处沿顺时针运动到B处,则它通过的路程、位移大小分别是(  )

A.

3πR
2
3πR
2

B.

3πR
2
2
R

C.

2
R、
2
R

D.

2R、
3πR
2

答案

从A处沿顺时针运动到B处时,质点经过了

3
4
个圆周,所以经过的路程为
3
4
×2πR=
3
2
πR,

位移是指从初位置到末位置的有向线段,所以从A到B的位移为AB之间的直线的距离,大小为

2
R.所以B正确.

故选B.

完形填空

E

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有多余选项。

Getting your children to study can be a little like getting them to eat their vegetables.

71   Make a study time and have it at  the same time every day. This will help your kids to learn to schedule their day and will give them a sense of control over how they spend their time.

Allow them to study in blocks of time, such as for half an hour with a five-minute break in the middle.    72   ideal (理想的)study times are after dinner or right after school before dinner.

Never allow your children to study in front of the television, as that will encourage passive activity.   73   

You’ll also need to help your kids find the right place to study. After you’ve set up a good study time for little learners, set up a good place where they can get those creative juices flowing.

74   Make sure there is a table or a desk and a comfortable chair.

75   This includes helping them out with their homework sometimes and being there for them with the answers to any questions. The input you give your children during study periods will help form a bond and help make studying enjoyable.

A.One of the best ways to form good study habits for your kids is to design a schedule that they keep to.

B.Finally, spend time with your kids when they’re studying.

C.Pick a place where your children can study properly.

D.Keep the atmosphere light and offer lots of encouragement, too.E. Instead, use TV as a treat or a reward when the homework is completed.

F. Try to stop this bad habit by offering some sort of reward.

G. Hold them to the schedule they create for themselves

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