问题 多选题

如图所示,滑块A和B叠放在固定的斜面体上,从静止开始以相同的加速度一起沿斜面加速下滑.已知B与斜面体间光滑接触,则在AB下滑的过程中,下列说法正确的是(  )

A.B对A的支持力不做功

B.B对A的作用力不做功

C.B对A的摩擦力做正功

D.B对A的摩擦力做负功

答案

A、B对A的支持力竖直向上,A和B是一起沿着斜面下滑的,所以B对A的支持力与运动方向之间的夹角大于90°,所以B对A的支持力做负功,所以A错误.

B、B对A的作用力包括B对A的支持力和摩擦力的作用,它们的合力的方向垂直斜面向上,与运动的方向垂直,所以B对A的作用力不做功,故B正确.

C、B对A的摩擦力是沿着水平面向左的,与运动方向之间的夹角小于90°,所以B对A的摩擦力做正功,故C正确.

D、由C的分析,可知D错误.

故选:BC

阅读理解

We all know that theme parks are places to have fun and amuse ourselves, but among so many exciting rides there are also some dangers, Make sure you know what the safety standards are for all the attractions at the park. If you do that , you will be safe and have fun.

Drink water. Believe it or not , dehydration-- when your body doesn’t have enough water--is the commonest cause of injuries at theme parks. Drinking water while you are at the park is not enough.You must make sure that you drink enough water before your visit.

Use your “common sense”. There are lots of people around , so make sure where your friends or family are .Also ,if you are walking and want to stop , make sure nobody is walking behind you. First step aside,then look behind and if you aren’t in anybody’s way,then stop.It might sound exaggerated(夸张的),but crashes between people can cause accidents.

Follow the instructions. The majority of theme parks have instructions for each ride. Some rides only allow people of a certain height. So make sure you are not too tall or too short before boarding any ride. Also, people with certain diseases or conditions are advised not to go on some rides. Do remember : If you are told not to go on a ride, then DON’T.

Do not ride with a bad atomach or if you’ve just eaten. Rides can make you ill because of their violent changes of direction and your lunch may end up on someone else’s head: surely not a very pleasant experience.

Have fun, relax, and be a little brave!

Some rides might look scary but theme parks are very safe places.

小题1:What is the leading reason for injuries at theme parks?

A.Snow

B.Dehydration

C.Fire

D.Crashes小题2:According to the author,____.

A.it doesn’t pay to go to theme parks

B.people can have lots of fun in theme parks

C.men are more interested in theme parks than women

D.shy people should not go to theme parks小题3:Which of the following will the author accept?

A.Children should notplay in theme parks.

B.One shouldn’t eat anything before riding.

C.One must always stay with his friends or family in theme parks.

D.One must read the instructions before playing in theme parks.

单项选择题