如图所示,是小型建筑工地上使用的罐笼式提升机,用它能把建筑材料从低处提升到高处.如果罐笼A(包括动 (2014?工业园区模拟)如图所示,是小型建筑工地使用的罐笼...
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(1)拉力移动的距离:s=2h=2×10m=20m;拉钢绳的速度:v=
s |
t |
20m |
20s |
(2)G=(mA+m材料)g=(150kg+250kg)×10N/kg=4000N,所以钢丝绳的拉力F=
1 |
2 |
(3)拉力做的功:W=Fs=2000N×20m=40000J=4×104J;
(4)拉力做的功就是总功:W总=4×104J,
材料升高10m做的功是有用功:G材料=m材料g=250kg×10N/kg=2500N,
有用功:W有用=G材料h=2500N×10m=2.5×104J,
则机械效率为:η=
W有 |
W总 |
2.5×104J |
4×104J |
答:(1)拉钢绳的速度为1m/s;
(2)钢丝绳的拉力为2000N;
(3)每提升1次建筑材料拉力F做的功为4×104J;
(4)该提升机的机械效率62.5%.
F=½G=½(150kg+250kg)×10N/kg=2000N
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