问题 选择题

如图所示,两个倾角分别为30°、45°的光滑斜面放在同一水平面上,两斜面间距大于小球直径,斜面高度相等,有三个完全相同的小球a、b、c.开始均静止于斜面同一高度处,其中b小球在两斜面之间.若同时释放a、b、c小球到达该水平面的时间分别为t1、t2、t3.若同时沿水平方向抛出,初速度方向如图所示,到达该水平面的时间分别为t1′、t2′、t3′.下列关于时间的关系正确的是(  )

A.t1>t3>t2

B.t1=t1′、t2=t2′、t3=t3

C.t1′>t3′>t2

D.t1<t1′、t2<t2′、t3<t3

答案

ABC

题目分析:第一种情况:b球做自由落体运动,a、c做匀加速运动.设斜面的高度为h,

则对a球:

, 对b球:    对c球:

由数学知识得:t1>t3>t2

第二种情况:a、b、c三球都沿水平方向有初速度,而水平方向不受力,故做匀速直线运动;

a、c小球沿斜面向下方向分运动不变,b球竖直方向分运动也不变,

故:t1=t1′、t2=t2′、t3=t3′.

阅读理解

阅读理解。

     It’s important to prepare(准备) for earthquakes because you don’t know where you will be when an

earthquake happens. Earthquakes may happen at any time, so prepare some things for your home, office

and car.

1. Clothes.

     If you live in a cold place, you must keep warm. You might not have heat after an earthquake.

     Think about your warm clothes.

2.Flashlights(手电筒) and spare batteries.

     Keep a flashlight beside you bed, at your office and in your car. Do not use matches(火柴) after an

earthquake until you are sure that no gas leaks(气体泄漏).

     Prepare a radio and some spare batteries. Most telephones will be out of order, so radios will be your best source of information(信息来源).

3. Food and medicine.

      It’s always a wonderful idea to keep some food on hand. For example, some biscuits, some canned

food, milk and some other drinks for at least 72 hours. You’d better get some necessary medicine for

our family.

4.Water.

     A person needs at least 1/2 gallon(加仑) of water daily just for drinking. Store at least 1 gallon of

water for a person every day and be prepared for 72 hours. It is suggested that you buy bottled water.

Do not open the bottle until you need it. Also, do check the “use by”date.

1.Why should people prepare themselves for an earthquake?

A.Because earthquakes can be know before they happen.

B.Because earthquakes usually take place in the neighborhood.

C.Because we don’t know when and where an earthquake will happen.

2.If you live in a cold place, you should prepare ________.

A. some hot water

B. some warm clothes

C. some batteries

3.According to the article we know that ________.

A.We need to prepare some things only at home

B.A telephone is the most important source of information

C.Flashlights but not matches are first used after earthquakes

4.You should prepare all of the following except ________.

A .milk

B. fresh vegetables

C. biscuits

5. About the water, which description is RIGHT?

A.A person should drink at least 1 gallon of water in a day.

B. You shouldn’t open the bottled water until you need it.

C. You’d better keep some hot water for 72 hours.

问答题 案例分析题