问题 问答题

全世界石油、煤炭消耗量的迅速增长,导致全球能源危机加剧.因此开发和利用新能源,成为全世界最为关注的问题之一.小明家的太阳能热水器内装有100kg、25℃的水,经过一天照射后,温度升高到75℃.[假设煤烧水时有效利用的热量占煤燃烧放出热量的10%,且已知水的比热容是4.2×103J/(kg•℃)]、煤的热值是3.0×107J/kg,则:

(1)水升温吸收的热量为多少焦?

(2)至少可以节约煤的质量是多少千克?

答案

(1)∵c=4.2×103J/(kg•℃),m=100kg,△t=75℃-25℃=50℃,

∴水吸收的热量为:Q=cm△t=4.2×103J/(kg•℃)×100kg×50℃=2.1×107J.

(2)而煤烧水时有效利用的热量占煤燃烧放出热量的10%,

∴煤完全燃烧放出的热量为:Q=

Q
10%
=
2.1×107J
10%
=2.1×108J,

而q=3.0×107J/kg,

∴需要煤的质量为:m=

Q
q
=
2.1×108J
3.0×107J/kg
=7kg.

答:(1)水温升高吸收的热量为2.1×107J;

(2)至少可以节约煤的质量是7kg.

多项选择题
单项选择题

Children start out as natural scientists, eager to look into the world around them. Helping them enjoy science can be easy; there’s no need for a lot of scientific terms or expensive lab equipment. You only have to share your children’s curiosity. Firstly, listen to their questions. I once visited a classroom of seven-year-olds to talk about science as a job. The children asked me "textbook questions" about schooling, salary and whether I liked my job. When I finished answering, we sat facing one another in silence. Finally I said, "Now that we’re finished with your lists, do you have questions of your own about science"

According to the passage, children can answer questions in a more logical, complete and creative way if adults ______.
A. ask them to answer quickly
B. wait for one or two seconds after a question
C. tell them to answer the next day
D. wait at least for three seconds after a question

After a long pause, a boy raised his hand, "Have you ever seen a grasshopper eat When I try eating leaves like that, I get a stomachache. Why"
This began a set of questions that lasted nearly two hours.
Secondly, give them time to think. Studies over the past 30 years have shown that, after asking a question, adults typically wait only one second or less for an answer, no time for a child to think. When adults increase their "wait time" to three seconds or more, children give more logical, complete and creative answers.
Thirdly, watch your language. Once you have a child involved in a science discussion, don’t jump in with "That’s right" or "Very good". These words work well when it comes to encouraging good behavior. But in talking about science, quick praise can signal that discussion is over. Instead, keep things going by saying "That’s interesting" or "I’d never thought of it that way before", or coming up with more questions or ideas.
Never push a child to "Think". It doesn’t make sense, children are always thinking, without your telling them to. What’s more, this can turn a conversation into a performance. The child will try to find the answer you want, in as few words as possible, so that he will be a smaller target for your disagreement.
Lastly, show; don’t just tell. Real-life impressions of nature are far more impressive than any lesson children can learn from a book or a television program. Let children look at their fingertips through a magnifying glass, and they’ll understand why you want them to wash before dinner. Rather than saying that water evaporates, set a pot of water to boil and let them watch the water level drop.