问题 实验题

(6分)在做《研究匀变速直线运动》的实验时,某同学得到一条用打点计时器打下的纸带如图所示,并在其上取了A、B、C、D、E、F、G等7个计数点,每相邻两个计数点之间还有4个点,图中没有画出,打点计时器接周期为T=0.02s的交流电源。经过测量得:d1=3.62cm,d2=8.00cm,d3=13.2cm,d4=19.19cm,d5=25.99cm,d6=33.61cm。

(1)计算vF=_____________

(2)物体的加速度=____________

(3)如果当时电网中交变电流的频率是,而做实验的同学并不知道,那么加速度的测量值与实际值相比_____________(选填:偏大、偏小或不变)。

答案

(1)0.72;(2)0.80;(3)偏小。

题目分析:(1)F点的速度为vF==0.721m/s;

(2)物体的加速度==0.80m/s2

(3)由于频率变大,故周期变小,两点间的时间变小,而我们仍按较大的值计算,可见计算时的时间偏大,故计算出的加速度的值偏小。

综合
单项选择题

Are you a man or a mouse When people ask this question they want to know (1) you think you are a (2) person or a coward. But you will never really know the answer to this question (3) you are tested in real life. Some people (4) they are brave but when they come face to face with real (5) , they act like cowards. Others think of themselves as cowards, but when they meet danger, they act like (6) .Lenny had always thought of himself as a (7) person. He got worried before examinations. He worried about his job and health. All he wanted in life was to be safe and healthy. (8) , on January 15th, 2002, a plane crashed into the Potomac River in Washington. Lenny went to the river to See what was happening. He saw a woman in the (9) water. Lenny did not feel afraid. He kept very (10) and did a very dangerous thing. He jumped into the Potomac, (11) to the woman, and kept her head (12) the water. Seventy-eight people died that day. Thanks to Lenny, it was not (13) .When you are in a very (14) situation and feel afraid, the body automatically produces a chemical in the blood. The chemical is called adrenalin. (15) adrenalin in the blood system, you actually feel per and per and are (16) to fight or run away. However, when you are absolutely terrified, the body can produce too much adrenalin. Where this (17) , the muscles become very hard and you find you (18) move at all. You are then paralyzed with fear. This is (19) when we are very frightened, we sometimes say we’re "petrified". This word comes from the Greek word "petros", which means "stone". We are (20) frightened that we become stonelike.

 

第(13)空应选择()

A.an accident

B.a mistake

C.seventy-eight

D.seventy-nine