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问题 计算题

如图是某太阳能热水器，向其中注入50kg的水，阳光照射—段时间后，水温从10℃升高到50℃．水的比热容是4.2×103J／（kg·℃）．试求：

（1）这段时间该热水器中的水吸收的热量是多少?

（2）如果这段时间该太阳能热水器接收到太阳辐射的热量是2.8× 107J，则这段时间该热水器的效率是多少?

（3）若用天然气来提供2.8×l07J的热量，需完全燃烧多少m3的天然气．（天然气的热值为8.4×l07J／m3，天然气完全燃烧放出的热量全部给水吸收．保留两位小数．）

答案

（1）8.4×106J；（2）30%；（3）0.33m3

题目分析：（1）Q吸=cm(t-t0)=4.2×103×50×(50-10)J=8.4×106J         2分

（2）η= Q吸/ Q接=8.4×106J /2.8× 107J =30%     2分

（3）m=Q/q=2.8×l07/8.4×l07m3=0.33m3      2分

点评：本题考查了学生对吸热公式、燃料完全燃烧放热公式、效率公式的掌握和运用，因条件已给出，难度不大．

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