问题 实验题

在“测滑轮组机械效率”的实验中,小强先用弹簧测力计测出钩码重力G,按图甲所示组装好器材,拉动弹簧测力计使钩码上升,用刻度尺分别测出钩码上升的高度h和绳端移动的距离s,在物体静止时读出拉力的大小F,下表是他记录的一组数据.

(1) 实验中拉动钩码上升时应____________拉动测力计;该实验的实验原理是___________.

(2) 由表中数据可计算出,滑轮组对钩码做的有用功为__________J,总功为_________J. (3) 对以上两个计算结果进行比较,其不合理之处是                    ;结合图甲弹簧测力计放大图,可知小强的错误是                       .(4) 同组的小华多用了一个相同的滑轮组成了图乙所示的滑轮组来提升相同的钩码时,发现更省力,那么用小华的方法测出的机械效率比小强的将__________(选填“偏大”,“偏小”,“不变”),其原因是__________________________________________________.(不计绳重和摩擦)

答案

(1)匀速     (2)0.1J    0.06J (3)总功小于有用功 读数时分度值读错了 (4)偏小  做相同的有用功时,乙图做的额外功更多

题目分析:(1)实验中拉动钩码上升时应匀速拉动测力计;实验原理是:

(2)W有用=Gh=2N×0.05m=0.1J;W=Fs=0.4N×0.15m=0.06J;

(3)由(2)知,计算出的总功小于有用功,这是不合理的;由图甲知,测力计的分度值为0.2N,所以测力计的读数应为0.8N,而不是0.4N;

(4)由乙图知,小华多用了一个动滑轮,所以做相同的有用功,小华做的额外功更多,所以机械效率会更低.

阅读理解

阅读理解。

     Car sharing is another way to drive green which is gaining in popularity, especially in urban areas. People

who may not drive every day but still want a car to run errands (差事) or drive on weekends benefit most

from car sharing. Car sharing is usually run by a service like Zipcar, though there are nonprofit (非营利的)

and informal car sharing services. Members pay a monthly fee and have access to an entire fleet of cars when

they need one. The cars are parked in fixed spots around the city, so members only need to make a reservation,

and then go to the pick up spot.

     Car sharing has major environmental benefits because it reduces the number of cars on the road. Members

don't drive just because they are in a car. They plan trips, and if they don't need a car, they don't use one. Still,

a car is available to them if they need to make a big trip to the grocery store, pick someone up at the airport or

if they want to go to the beach for the day. Members also benefit by having access to a car without any of the

headaches of ownership. They usually don't have to pay for the gas, insurance or maintenance (保养), and the

monthly membership fee is less than a typical car payment. So if you really want to go green but aren't ready

to totally give up a car yet, car sharing may be the way to go.

     If you still need to get around, but want to go even greener than sharing a car, share a bus!

1. The author intends to tell us that car sharing ____.

A. has become the most popular way to go to work

B. has become the best way to cut living costs

C. is becoming more and more popular in cities

D. is becoming popular both in urban and rural (乡村的) areas

2. We can learn from the passage that ____. 

A. Zipcar can't help you if you are running urgent errands

B. Zipcar, different from other services, is aimed at green driving with no profit

C. Zipcar is a company supplying car sharing services for a monthly payment

D. Zipcar is a company providing formal car sharing free

3. The second paragraph mainly tells us ____.

A. why people will share a car

B. why car sharing benefits the environment

C. why car sharing is cheaper than owning a car

D. why a car is available to members

4. Which of the following is NOT mentioned in the passage?

A. Car sharing has become a new trend (趋势).

B. Car sharing can save you the headaches of ownership.

C. Bus sharing is even greener than car sharing.

D. Zipcar is the largest company offering car sharing services.

单项选择题 A1/A2型题