题干

如图,东湖中学想用离心泵将湖中的水抽到C处的养鱼池中.要求在30min内至少向养鱼池中输水120m3,学校领导将以下几个需要解决的问题交给了科技小组.

(1)A,B处各有一个平台,离心泵应放在什么位置,请说明理由.

(2)如果某型号离心式水泵的扬程为15m,功率为17kW,效率为0.6,试通过计算说明这台水泵是否可满足东湖中学的需求?

(3)为了节约资金,有人提出全部采购比硬质管便宜、而且与水泵管径相符的软橡皮管配套使用,你认为是否可行,为什么?说出你的正确方案.

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答案(点此获取答案解析)

解:(1)因为泵的总扬程=吸水扬程+压水扬程,离心式水泵的吸水扬程是由大气压决定的,当

大气压为标准大气压时,吸水扬程实际不会超过10m.所以泵不能放在B处,只能放在A处.

(2)不考虑水的动能:①增加的势能按13.8m计算:

已知t=30min=1800s,h=13.8m.V=120m3,η=0.6.

则W有=mgh=ρ水Vgh=1.0×103kg/m3

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    Fear may be felt in the heart as well as in the head, according to a study that has found a link between the cycles of a beating heart and the chance of someone feeling fear.

    Tests on healthy volunteers found that they were more likely to feel a sense of fear at the moment when their hearts are contracting(收缩)and pumping blood around their bodies, compared with the point when the heartbeat is relaxed. Scientists say the results suggest that the heart is able to influence how the brain responds to a fearful event, depending on which point it is at in its regular cycle of contraction and relaxation.

    Sarah Garfinkel at the Brighton and Sussex Medical School said: “Our study shows for the first time that the way in which we deal with fear is different depending on when we see fearful pictures in relation to our heart.”

    The study tested 20 healthy volunteers on their reactions to fear as they were shown pictures of fearful faces. Dr Garfinkel said, “The study showed that fearful faces are better noticed when the heart is pumping than when it is relaxed. Thus our hearts can also affect what we see and what we don't see and guide whether we see fear.”

    To further understand this relationship, the scientists also used a brain scanner(扫描仪)to show how the brain influences the way the heart changes a person's feeling of fear.

    “We have found an important mechanism by which the heart and brain ‘speak' to each other to change our feelings and reduce fear,” Dr Garfinkel said.

    “We hope that by increasing our understanding about how fear is dealt with and ways that it could be reduced, we may be able to develop more successful treatments for anxiety disorders, and also for those who may be suffering from serious stress disorder.”