图是某建筑工地提升建材所用的升降机示意图。建材的重力是6300N,建材与货箱水平底面的接触面积是1.2m 2 某建筑工地用升降机提升实心砖的示意图如图所示.升降机货箱的重...

\uff082010?\u5927\u8fde\uff09\u67d0\u5efa\u7b51\u5de5\u5730\u7528\u5347\u964d\u673a\u63d0\u5347\u5b9e\u5fc3\u7816\u7684\u793a\u610f\u56fe\u5982\u56fe\u6240\u793a\uff0e\u5347\u964d\u673a\u8d27\u7bb1\u7684\u91cd\u529b\u662f300N\uff0cg\u53d610N/kg\uff0e\u4e0d\u8ba1

\uff081\uff09\u7816\u7684\u5bc6\u5ea6\uff1a\u03c1=2\u00d7103kg/m3\u6bcf\u5757\u8f6c\u7684\u4f53\u79ef\uff1aV=1.5\u00d710-3m3\u6bcf\u5757\u7816\u7684\u8d28\u91cf\uff1am=\u03c1V=2\u00d7103kg/m3\u00d71.5\u00d710-3m3=3kg\u6bcf\u5757\u7816\u7684\u91cd\u529b\uff1aG=mg=3kg\u00d710N/kg=30N\uff1b\uff082\uff09\u8d27\u7bb1\u7684\u603b\u91cd\uff1aG\u603b=3\u00d7F\u62c9=3\u00d72100N=6300N\u7816\u7684\u603b\u91cd\uff1aG\u7816=G\u603b-G\u7bb1=6300N-300N=6000N\u7816\u7684\u5757\u6570\u662f\uff1a6000N30N=200\u5757\uff1b\uff083\uff09\u94a2\u4e1d\u7ef3\u79fb\u52a8\u7684\u8ddd\u79bb\uff1aL=10m\u00d73=30m\u94a2\u4e1d\u7ef3\u7684\u62c9\u529b\uff1aF\u62c9=2000N\u62c9\u529b\u505a\u7684\u529f\uff1aW=F\u62c9L=2000N\u00d730m=60000J\u62c9\u529b\u505a\u7684\u529f\u7387\uff1aP=Wt=60000J50s=1200W\uff1b\u7b54\uff1a\uff081\uff09\u5757\u7816\u7684\u91cd\u529b\u662f\uff1a30N\uff1b\uff082\uff09\u5347\u964d\u673a\u4e00\u6b21\u6700\u591a\u80fd\u5300\u901f\u63d0\u5347200\u5757\uff1b\uff083\uff09\u94a2\u4e1d\u7ef3\u7684\u62c9\u529b\u7684\u529f\u7387\u662f\uff1a1200W\uff0e

\u89e3\uff1a\uff081\uff09\u7816\u7684\u5bc6\u5ea6\uff1a\u03c1=2\u00d710 3 kg/m 3 \u6bcf\u5757\u8f6c\u7684\u4f53\u79ef\uff1aV=1.5\u00d710 \ufe633 m 3 \u6bcf\u5757\u7816\u7684\u8d28\u91cf\uff1am=\u03c1V=2\u00d710 3 kg/m 3 \u00d71.5\u00d710 \ufe633 m 3 =3kg \u6bcf\u5757\u7816\u7684\u91cd\u529b\uff1aG=mg=3kg\u00d710N/kg=30N\uff082\uff09\u8d27\u7bb1\u7684\u603b\u91cd\uff1aG \u603b =3\u00d7F \u62c9 =3\u00d72100N=6300N\u7816\u7684\u603b\u91cd\uff1aG \u7816 =G \u603b \ufe63G \u7bb1 =6300N\ufe63300N=6000N \u7816\u7684\u5757\u6570\u662f\uff1a =200\u5757\uff083\uff09\u94a2\u4e1d\u7ef3\u79fb\u52a8\u7684\u8ddd\u79bb\uff1aL=10m\u00d73=30m\u94a2\u4e1d\u7ef3\u7684\u62c9\u529b\uff1aF \u62c9 =2000N \u62c9\u529b\u505a\u7684\u529f\uff1aW=F \u62c9 L=2000N\u00d730m=60000J \u62c9\u529b\u505a\u7684\u529f\u7387\uff1aP= = =1200W

解:(1)p=F/S=G/S =6300N/1.2m 2 =5250Pa       (2分)
(2)由P=W/t可得,F所做的功W F =Pt=1800W×60s=1.08×10 7 J(2分)
(3)W=FS可得
W =Gh=6300N×12m=7.56×10 4 J     (1分)
W = W F =1.08×10 7 J
η= W / W = W /W F  ="7.56×104J/1.08×107" J=70%   (2分)
答:(1)建材对货箱水平底面的压强是5250Pa。
(2)拉力F所做的功是1.08×107 J。
(3)该滑轮组提升这些建材的机械效率是70% 。

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