上周学校购买了一批水龙头，据商家说其材料铜质的，实验室的老师组织九年级的一些同学通过实验来验证商家的说法。他们把一个水龙头用轻质细线捆好后挂在弹簧测力计上，在空气中测得它的重力为1.6N，再把这个水龙头浸没在水中，如图所示，这时弹簧测力计的读数为1.4N（ρ铜=8.9×103kg/m3，g=10N/kg）。求：
（1）每个水龙头的质量是多少？
（2）这个水龙头浸没在水中时所受到的浮力有多大？
（3）这批水龙头的密度是多少？商家的说法是否正确？
解：
（1）m=G/g= 1.6N/10N/kg =0.16 kg=160 g；
（2）F浮=G-F=1.6N-1.4N=0.2N；
（3）∵F浮=ρ水gV排
∴V排== F浮/ρ水g = 0.2N/（103kg/m3×10N/kg） =2×10-5m3=20 cm3∴V = V排= 20 cm3
∴ρ=
=
=8g/cm3=8×103kg/m3，∵8×103kg/m3<8.9×103kg/m3，故：这批水龙头不是纯铜的。
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| People always say that the earlier one learns a language, the 1 it is to do so, in theory it is that, 2 , in my opinion, that refers to spoken la  nguage. Capability (能力) to practice some essential (基本的) 3 of a language and read between the lines can only be trained through proper reading ways and hard work 4 . So spending money to help 5 learn English may 6 up with disap  pointment. It is likely that the more you 7 , the more you are let down. The daughter of one of my friends 8 English in primary school, 9 her foreign teacher's blindness 10 psychology. She did not want to go on 11 English until middle school, 12 a college student studying English slowly 13 her interest in the language. It is better to have the child learn Chinese th  an to have some difficulty 14 learning English for several years. Having been engaged in English education, 15 find that despite(尽管) their excellent 16 , many students have 17 command of English words and phrases. So I suggest that children 18 classical Chinese prose(散文),rather than 19 them to learn English hurriedly. Otherwise, they may let go the best time to 20 the language ability of their mother tongue. | ||||
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