如图所示，某建筑工地用升降机提升大理石．当货箱内物体质量是360kg时，滑轮组的机械效率是80%，不计滑轮
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\uff081\uff09\u7531\u03c1=mV\u5f97\u6bcf\u5757\u5927\u7406\u77f3\u7684\u8d28\u91cf\uff1am1=\u03c1V=2.7\u00d7103kg/m3\u00d71.0\u00d710-2m3=27kg\u6bcf\u5757\u5927\u7406\u77f3\u91cd\uff1aG1=m1g=27kg\u00d710N/kg=270N\uff1b\uff082\uff0910\u5757\u5927\u7406\u77f3\u7684\u603b\u91cd\u529b\uff1aG=10G1=10\u00d7270N=2700N\uff0c\u7531\u56fe\u77e5\uff0cn=3\uff0c\u5219\u5347\u964d\u673a\u7684\u6548\u7387\uff1a\u03b7=W\u6709\u7528W\u603b\u00d7100%=GhFs\u00d7100%=GhF3h\u00d7100%=G3F\u00d7100%=2700N3\u00d71000N\u00d7100%=90%\uff1b\u2235\u4e0d\u8ba1\u94a2\u4e1d\u7ef3\u7684\u91cd\u529b\u548c\u6469\u64e6\uff0c\u2234F=13\uff08G+G\u52a8+G\u7bb1\uff09\uff0c\u5373\uff1a1000N=13\uff082700N+G\u52a8+200N\uff09\u52a8\u6ed1\u8f6e\u7684\u91cd\u529b\uff1aG\u52a8=100N\uff1b\uff083\uff09\u5f53\u94a2\u4e1d\u7ef3\u7684\u62c9\u529bF\u2032=1540N\u65f6\uff0c\u5373\uff1aF\u2032=13\uff08G\u2032+G\u52a8+G\u7bb1\uff09\uff0c1540N=13\uff08G\u2032+100N+200N\uff09\u89e3\u5f97\uff1aG\u2032=4320N\uff1b\u5927\u7406\u77f3\u7684\u5757\u6570\uff1aN=4320N270N=16\uff08\u5757\uff09\uff1b\u6709\u7528\u529f\u7387\uff1aP\u6709\u7528=W\u6709\u7528t=G\u2032ht=4320N\u00d715m60s=1080W\uff0e\u7b54\uff1a\uff081\uff09\u6bcf\u5757\u5927\u7406\u77f3\u7684\u91cd\u529b\u662f270N\uff1b\uff082\uff09\u5347\u964d\u673a\u6548\u7387\u4e3a90%\uff1b\uff083\uff09\u63d0\u5347\u5927\u7406\u77f316\u5757\uff0c\u5347\u964d\u673a\u7684\u6709\u7528\u529f\u7387\u662f1080W\uff0e
（1）货箱内物体质量m=360kg，
G=mg=360kg×10N/kg=3600N，
由图知，n=3，则拉力端移动的距离s=3h，
∵η=
| W有用 |
| W总 |
| Gh |
| Fs |
| Gh |
| F3h |
| G |
| 3F |
∴拉力F=
| G |
| 3η |
| 3600N |
| 3×80% |
（2）由题知，n=3，并且不计滑轮和钢丝绳的重力、不计摩擦，则拉力：
F=
| 1 |
| 3 |
即：1500N=
| 1 |
| 3 |
货箱重G货箱=900N，
当最大拉力F最大=2000N时，升降机提升的最大货物重G最大，则：
F最大=
| 1 |
| 3 |
即：2000N=
| 1 |
| 3 |
解得：
G最大=5100N；
（3）由（2）的计算可知，当拉力F=2000N，货物重G=5100N，
由图知，n=3，则s=3h=3×15m=45m，
有用功：
W有用=Gh=5100N×15m=76500J，
钢丝绳的拉力做的总功：
W总=Fs=2000N×45m=90000J，
钢丝绳的拉力的功率：
P=
| W总 |
| t |
| 90000J |
| 60s |
滑轮组的机械效率：
η=
| W有用 |
| W总 |
| 76500J |
| 90000J |
答：（1）拉力的大小是为1500N；
（2）该升降机一次最多能匀速提升5100N的货物；
（3）钢丝绳的拉力的功率是1500W；滑轮组的机械效率是85%．
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