(2013?房山区二模)如图所示,容器内装有适量水,滑轮组的动滑轮质量为m0,质量为m1的物体A经一轻质弹簧 (2010?房山区一模)如图所示,水平桌面上放一底面积为10...

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\uff081\uff09\u7531\u56fe\u793a\u6ed1\u8f6e\u7ec4\u53ef\u77e5\uff0c\u6ed1\u8f6e\u7ec4\u627f\u91cd\u7ef3\u5b50\u7684\u80a1\u6570n=2\uff0c\u8bbe\u7ef3\u5b50\u7684\u62c9\u529b\u4e3aT\uff0c2T=F+G\u52a8\u6ed1\u8f6e\uff0c\u7ef3\u5b50\u62c9\u529bT1=F1+G\u52a8\u6ed1\u8f6e2=11.8N+1N2=6.4N\uff0cT2=F2+G\u52a8\u6ed1\u8f6e2=13.4N+1N2=7.2N\uff0c\u91cd\u7269\u9759\u6b62\uff0c\u5904\u4e8e\u5e73\u8861\u72b6\u6001\uff0c\u5219G=F\u6d6e+T\uff0c\u2235\u03c1=mV\uff0c\u2234\u7269\u4f53\u91cd\u529bG=mg=\u03c1gV\uff0c\u7269\u4f53\u5728\u6db2\u4f53\u4e2d\u53d7\u5230\u7684\u6d6e\u529bF\u6d6e=\u03c1\u6db2gV\u6392\uff0c\u8bbe\u7269\u4f53\u7684\u4f53\u79ef\u4e3aV\uff0c\u7269\u4f53\u5bc6\u5ea6\u4e3a\u03c1\uff0c\u7531G=F\u6d6e+T\u5f97\uff1a\u03c1gV=\u03c1\u6db2gV+T1\uff0c\u03c1gV=\u03c1\u6db2gV2+T2\uff0c5.0\u00d7103kg/m3\u00d710N/kg\u00d7V=\u03c1\u6db2\u00d710N/kg\u00d7V+6.4N \u2460\uff0c5.0\u00d7103kg/m3\u00d710N/kg\u00d7V=\u03c1\u6db2\u00d710N/kg\u00d7V2+7.2N \u2461\uff0c\u75312\u2461-\u2460\u89e3\u5f97\uff1aV=1.6\u00d710-4m3\uff0c\u5c06V\u4ee3\u5165\u2460\u89e3\u5f97\uff1a\u03c1\u6db2=1\u00d7103kg/m3\uff1b\u7269\u4f53\u7684\u91cd\u529bG=\u03c1gV=5.0\u00d7103kg/m3\u00d710N/kg\u00d71.6\u00d710-4m3=8N\uff1b\uff082\uff09\u7531\uff081\uff09\u53ef\u77e5\uff0c\u6db2\u4f53\u7684\u5bc6\u5ea6\u4e3a\u03c1\u6db2=1\u00d7103kg/m3\uff1b\uff083\uff09\u5f53\u7269\u4f53\u4e0a\u63d0\u523012\u4f53\u79ef\u9732\u51fa\u6db2\u9762\u65f6\uff0c\u6db2\u4f53\u6df1\u5ea6\u7684\u53d8\u5316\u91cf\uff1a\u25b3h=\u25b3VS\u5bb9\u5668=V2S\u5bb9\u5668=1.6\u00d710?4m32\u00d7100\u00d710?4m2=8\u00d710-3m\uff0c\u6db2\u4f53\u538b\u5f3a\u7684\u53d8\u5316\u91cf\u25b3p=\u03c1g\u25b3h=1\u00d7103kg/m3\u00d710N/kg\u00d78\u00d710-3m=80Pa\uff0c\u7269\u4f53\u63d0\u51fa\u6db2\u9762\uff0c\u7269\u4f53\u6392\u5f00\u6db2\u4f53\u7684\u4f53\u79ef\u53d8\u5c0f\uff0c\u6db2\u9762\u4e0b\u964d\uff0c\u5f53\u7269\u4f53\u4e0a\u63d0\u523012\u4f53\u79ef\u9732\u51fa\u6db2\u9762\u65f6\u6db2\u4f53\u5bf9\u5bb9\u5668\u5e95\u7684\u538b\u5f3a\uff1ap\u2032=p-\u25b3p=2000Pa-80Pa=1920Pa\uff1b\u7b54\uff1a\uff081\uff09\u7269\u4f53\u7684\u91cd\u529b\u4e3a8N\uff1b\uff082\uff09\u6db2\u4f53\u7684\u5bc6\u5ea6\u4e3a1\u00d7103kg/m3\uff1b\uff083\uff09\u5f53\u7269\u4f53\u4e0a\u63d0\u523012\u4f53\u79ef\u9732\u51fa\u6db2\u9762\u65f6\u6db2\u4f53\u5bf9\u5bb9\u5668\u5e95\u7684\u538b\u5f3a\u4e3a1920Pa\uff0e

(1)物体B浸没在水中受到的浮力:
FgVB=1×103kg/m3×10N/kg×2×10-3m3=20N,
弹簧的拉力F=10N/cm×2cm=20N,
由图示滑轮组公式可知,滑轮组承重绳子的有效股数n=2,
在挂钩上悬挂重物C时,由平衡条件得:
nm3g=(m0+m1)g+F,即2×1.6kg×10N/kg=(m0+m1)×10N/kg+20N,
F+F=m2g,20N+20N=m2g,解得:m0+m1=1.2kg,m2=4kg,
挂上重物D时,由平衡条件得:
n(m1+m3)g=(m0+m1+m2)g,即:2×(m1+1.6kg)=m0+m1+4kg,
解得m0=0.2kg,m1=1kg,
滑轮组的效率η=
W有用
W
=
W有用
W有用+W
=
(m1+m2)h
(m1+m2)h+m0h
=
1kg+4kg
1kg+4kg+0.2kg
≈96%;
(2)重物D的速度vD=nvB=2×0.1m/s=0.2m/s,
重力GD所做功的功率P=GDvD=(m1+m3)gvD=(1kg+1.6kg)×10N/kg×0.2m/s=5.2W;
答:(1)滑轮组的机械效率为96%;
(2)重力GD所做功的功率为5.2W.

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