问题 问答题

如图所示,是一提升重物用的直流电动机工作时的电路图.电动机内电阻r=0.8Ω,电路中另一电阻R=10Ω,直流电压U=160V,电压表示数UV=110V.试求:

(1)通过R的电流;

(2)输入电动机的电功率;

(3)若该电动机以v=1m/s匀速竖直向上提升一重物,求此重物的质量?(g取10m/s2

答案

(1)通过R的电流 I=

U1-U2
R
=
160-110
10
A=5A;

(2)电动机的输入功率 P1=U2I=110×5W=550W,

(3)电动机内电阻的发热功率 P2=I2r=52×0.8W=20W,

输出的机械功率 P3=P1-P2=(550-20)W=530W;

而P3=Fv=mgv

解得:m=

530
10×1
=53kg

答:

(1)通过R的电流为5A;

(2)输入电动机的电功率为550W;

(3)若该电动机以v=1m/s匀速竖直向上提升一重物,此重物的质量为53kg.

完形填空

阅读下面的短文,并根据文章后的题目要求回答小题。

(1)While adults need to eat breakfast each day to perform their best, kids need it even more. Their growing bodies and developing brain rely heavily on the regular intake of food. When kids skip breakfast , they can end up going for as long as eighteen hours without food. This period of semi-starvation can create a lot of physical, intellectual, and behavioral problems for them.

(2)If you and your kids regularly skip breakfast to save time or to get a few more minutes of sleep, remember that eating a healthy morning meal will probably save your time in the long run. By recharging your brain and your body, you’ll be more efficient in just about everything you do.

(3)Interestingly, studies show that kids who skip breakfast are late for and absent from school more often than children who eat breakfast on a regular basis. Time invested in breakfast is much more valuable than the few extra minutes of sleep you might get by skipping the morning meal. If you and your kids seem unable to make time for breakfast, consider enrolling your children in a school breakfast program. If possible, pack a breakfast brown-bag the night before so that you and your kids can eat on the way to school and work.

(4)Some people skip breakfast in an effort to lose weight, but actually it is more likely to cause weight gain rather than weight loss. Skipping breakfast is strongly linked to the development of obesity. According to research, skipping meals, especially breakfast, can actually make weight control _______________. Breakfast skippers tend to eat more food than usual at the next meal or eat high-calorie snacks to get rid of hunger.

(5)To teens, especially teenage girls, skipping breakfast may seem like a perfect way to lose weight. It’s important for moms to educate their kids about the importance of the morning meal and role it plays in maintaining good health and preventing obesity.

1. What is mainly discussed in the passage? (no more than 6 words)

_______________________________________________________________________________

2. Complete the following statement with proper words. (no more than 3 words)

Sparing some time ______________ is more beneficial to you than skipping it for more sleep.

3. List three reasons why many kids and adults skip breakfast. (no more than 10 words)

_______________________________________________________________________________

4.Fill in the blank in Paragraph 4 with proper words. (no more than 4 words)

____________________________________________________________________________

5. What does the underlined word “it” in the last paragraph probably refer to? (no more than 3 words)

_______________________________________________________________________________

问答题 简答题