1/5单选题
难度：
1.如图所示，小华用60N的拉力匀速提升一个重为120N的物体，不计绳重和摩擦，则滑轮组的机械效率为 （ ）
| A | 80% |
| B | 66.7% |
| C | 76.6% |
| D | 50% |
- 提示1：
- IOacieeUqOWKn+aYr+WFi+acjeeJqeS9k+mHjeWKm+WBmueahOWKnw==
- 提示2：
- IOaAu+WKn+aYr+aLieWKm+WBmueahOWKnw==
- 提示3：
- IOeJqeS9k+enu+WKqOeahOi3neemu+aYr+e7s+WtkOenu+WKqOi3neemu+eahOS4ieWIhuS5i+S4gA==
正确答案：Qg==
PGRpdj7op6PvvJpX5pyJPUdoPTEyME5oLFfmgLs9RnM9NjBOw5czaD0xODBOaC7miYDku6XmnLrmorDmlYjnjoc9MTIwTmgvKDE4ME5oKT02Ni43JTwvZGl2Pg==
2/5单选题
难度：
2.工人用如图所示的滑轮组匀速提起一个重为200N的物体A，动滑轮重50N ， 不计绳重和摩擦，滑轮组的机械效率为η1 。 用同一装置提升物体B，滑轮组的机械效率为η2 ，η1：η2=4:3则B的重力为（ ）
| A | 120N |
| B | 75N |
| C | 150N |
| D | 60N |
- 提示1：
- IOWIhuWIq+eUqOWFrOW8j+ihqOekuuWHuuS4pOS4quacuuaisOaViOeOhw==
- 提示2：
- IOWIqeeUqOacuuaisOaViOeOh+avlOi/m+ihjOWIhuaekOOAgg==
- 提示3：
- IOazqOaEj++8jOWQjOS4gOijhee9rueahOWKqOa7kei9rueahOmHjeWKm+ebuOWQjA==
正确答案：Qg==
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
3/5单选题
难度：
3.小军用如图所示的装置提升重物A，已知：小军的质量为60kg,mA=40kg,当小军用F1=100N的力拉绳时，他对地面的压强为
,当小军用大小为F2的力拉绳时，他对地面的压强为
，重物匀速上升，不计绳重和摩擦，则滑轮组的机械效率为（ ）（g=10N/kg）
,当小军用大小为F2的力拉绳时，他对地面的压强为，重物匀速上升，不计绳重和摩擦，则滑轮组的机械效率为（ ）（g=10N/kg） | A | 75% |
| B | 80% |
| C | 76.6% |
| D | 71.4% |
- 提示1：
- IOWvueWwj+WGm+WPl+WKm+WIhuaekO+8jOaxguWHuuS7luWvueWcsOmdoueahOWOi+WKmw==
- 提示2：
- IOeUseWOi+W8uuaxguWHuuWKqOa7kei9rueahOmHjeWKm+WSjEY8c3ViPjI8L3N1Yj7nmoTlpKflsI/jgII=
- 提示3：
- IOeUseWFrOW8j+axguacuuaisOaViOeOhw==
正确答案：RA==
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
4/5单选题
难度：
4.甲、乙二人用如图所示装置提升重为1920N的货箱。两人同时用等大的力竖直向下拉绳； G甲：G乙=4:3，提升时地面对甲乙的支持力N1:N2=5:3，已知：N2=300N ，此装置中两个滑轮组的规格完全相同。不计绳重和摩擦。此装置的机械效率为（ ）
| A | 82% |
| B | 85% |
| C | 80% |
| D | 88% |
- 提示1：
- IOeUseW3suefpeWPr+W+l++8jE48c3ViPjI8L3N1Yj49MzAwTu+8jE48c3ViPjE8L3N1Yj49NTAwTg==
- 提示2：
- IOiuvuaLieWKm+S4ukbvvIzliJnmnInvvJpHPHN1Yj7nlLI8L3N1Yj4tRj01MDBO77yMRzxzdWI+5LmZPC9zdWI+LUY9MzAwTu+8jOWPiEc8c3ViPueUsjwvc3ViPu+8mkc8c3ViPuS5mTwvc3ViPj00OjPvvIzmiYDku6XlvpdGPTMwME7vvIw=
- 提示3：
- IOeUseacuuaisOaViOeOh+WFrOW8j+WPr+axguW+l+OAgg==
正确答案：Qw==
PGRpdj7op6PvvJrnlLHlt7Lnn6Xlj6/lvpfvvIxOPHN1Yj4yPC9zdWI+PTMwME7vvIxOPHN1Yj4xPC9zdWI+PTUwME7vvIzorr7mi4nlipvkuLpG77yM5YiZ5pyJ77yaRzxzdWI+55SyPC9zdWI+LUY9NTAwTu+8jEc8c3ViPuS5mTwvc3ViPi1GPTMwME7vvIzlj4hHPHN1Yj7nlLI8L3N1Yj7vvJpHPHN1Yj7kuZk8L3N1Yj49NDoz77yM5omA5Lul5b6XRj0zMDBO77yM55Sx5py65qKw5pWI546H5YWs5byP5Y+v5rGC5b6Xzrc9PGltZyB3aWR0aD0xNCBoZWlnaHQ9NDIgc3JjPSJodHRwczovL3AxLnFpbmdndW8uY29tL0cxL00wMC8yMy9DMS9yQkFDRTFNTWVmLVJJaU11QUFBQlpuMzJHcDAzMTMucG5nIj49ODAl44CCPC9kaXY+
5/5单选题
难度：
5.小明用如图所示装置提升物体A，当小明用F1=100N的拉力拉绳时，B对地面的压力为400N，当用F2=150N的拉力拉绳时，物体A匀速上升。已知：GA:GB=5:6。不计绳重和摩擦，滑轮组的机械效率为（ ）
| A | 85% |
| B | 89% |
| C | 83.3% |
| D | 88.3% |
- 提示1：
- IOaKikHjgIFC5ZKM5Yqo5ruR6L2u55yL5oiQ5LiA5Liq5pW05L2T77yM6L+b6KGM5Y+X5Yqb5YiG5p6Q5b6X77yaRzxzdWI+Qjwvc3ViPitHPHN1Yj5BPC9zdWI+K0c8c3ViPkQ8L3N1Yj4tNDAwTj0yMDBOLA0K
- 提示2：
- IOWvuUHov5vooYzlj5flipvliIbmnpDlvpfvvJpHPHN1Yj5BPC9zdWI+K0c8c3ViPkQ8L3N1Yj49MsOXMTUwTg==
- 提示3：
- IOaxguW+l0c8c3ViPkE8L3N1Yj7lkoxHPHN1Yj5EPC9zdWI+77yM5YiZ5Y+v5qC55o2u5YWs5byP5rGC5b6X5py65qKw5pWI546H
正确答案：Qw==
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