(1)电火花计时器工作电源是______电源,当电源的频率为50Hz时,每隔0.

题型:填空题

问题:

(1)电火花计时器工作电源是______电源,当电源的频率为50Hz时,每隔0.02秒打一个点.

(2)实验装置如图1所示.一小车放在水平长木板上,左侧拴有一细软线,跨过固定在木板边缘的滑轮与一重物相连,小车右侧与穿过电火花计时器的纸带相连,在重物牵引下,小车在木板上向左运动.图2给出了电火花计时器在纸带上打出的一些计数点,相邻的两个计数点间的时间间隔为0.1s,相邻的两个计数点间的距离如图中所标.

①若认为某段时间内的平均速度等于这段时间中间时刻的速度,则打计数点1、3时小车对应的速度分别为:v1=______m/s,v3=______m/s,(小数点后保留二位)

②据此可求出小车从1到3计数点内的加速度为a=______m/s2

考点:实验:探究小车速度随时间变化的规律
题型:填空题

下列说法中正确的是(     )

A.所有原子的原子核都是由质子和中子构成

B.在同一种物质中同种元素的化合价可能不相同

C.由同一种元素组成的物质一定是单质,不可能是化合物

D.分子、原子都是不带电的粒子,所以不带电的粒子一定是分子或原子

题型:填空题

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。选项中有两项为多余选项。

Ali is from a Middle Eastern country. He now stays in the USA. He smokes a lot of cigarettes every day. He has smoked for nine years. Ali says, “I tried to quit smoking in my hometown, but it was impossible. My parents smoke. My brothers smoke. All my friends smoke. At parties and at meetings, almost all the men smoke. Here in the United States, not as many people smoke.小题1:    

Many smokers are like Ali: they want to stop smoking.     小题2:      They know it can cause cancer and heart disease. But it is difficult for them to give up smoking because cigarettes have a drug in them. The drug is nicotine. People who smoke a lot need nicotine.

 小题3:    The nicotine makes him sick. In a few days, the smoker's body is used to the nicotine, and he feels fine. Later, the smoker needs nicotine to keep feeling fine. Without nicotine, he feels bad.

 小题4:     Many people who quit will soon smoke again. At a party or at work they will decide to smoke "just one" cigarette. Then they will smoke another cigarette, and another. Soon they become smokers again.  小题5:    

A.It is very hard to quit smoking.

B.It will be easier to change the smoking habit here.

C.Thus nicotine makes smokers addicted to cigarettes.

D.The smokers know that smoking is bad for their health.E. When a person first begins to smoke, he usually feels terrible.

F. Maybe there is only one easy way to quit smoking: never start.

G. But it is said that medicine is needed to stop them from smoking.

题型:填空题

吸收塔收集池中的pH值通过注入()来进行控制。

A.石灰石浆液;

B.工艺水;

C.氧化空气;

D.石膏。

题型:填空题

必须选择预装配底漆,以使其有效于经过喷丸处理具有圆形锚链装外观的表面

题型:填空题

缓倾斜煤层的倾角一般为()。

A.0°-25°

B.4°-25°

C.8°-25°

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