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1、功和机械能单元测试题一(参考答案)DIV.MyFav_1326680514018 P.MsoNormalTEXT-JUSTIFY: inter-ideograph; FONT-SIZE: 10.5pt; FONT-FAMILY: Times New Roman; TEXT-ALIGN: justifyDIV.MyFav_1326680514018 LI.MsoNormalTEXT-JUSTIFY: inter-ideograph; FONT-SIZE: 10.5pt; FONT-FAMILY: Times New Roman; TEXT-ALIGN: justifyDIV.MyFav_1326
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7、题:(1-6小题单选、7-10小题多选)题号12345678910答案BDDACCBCBCACABCD二、填空题110 50W 12864J 80% 13动能和势能是可以相互转化的;由于空气摩擦,使得机械能减小 14大卡车 小 15机械能三、实验题16(1)控制变量法 (2)0.756 0.9 84% (3)结论一:在斜面的粗糙程度相同时,斜面的倾角越大,机械效率越高。结论二:在斜面的倾角相同时,斜面的粗糙程度越大,机械效率越低。17(1)ac 纸盒子被推动距离(2)让小球从斜面的同一高度由静止滚下(3)ab四、计算题18解:1.6t=1600Kg 108Km/h=30m/S 20min=1200s(1)F=f=0.1G=0.1mg=0.11600 Kg10N/Kg=1600N(2)W=FS=1600N30m/S1200s=5.76107J(3)P=W/S=5.76107J/1200s=4.8104J19解:绕法如图,绳子段数n=4。(1)因为,所以拉力为。由于,所以绳子自由端移动速度为,由于忽略摩擦及绳重,则。所以动滑轮重(2)减小由于忽略摩擦及绳重所以当提升的物体重力减小时,滑轮组机械效率减小。(或者当提升物体的重力减小时,有用功减小,额外功不变,故其机械效率减小。
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