(2012? Huaian) As shown in the figure, in the experiment to measure the mechanical efficiency of the lever, the spring dynamometer was pulled vertically upward at a uniform speed, so that the spring d

(2012? Huaian) As shown in the figure, in the experiment to measure the mechanical efficiency of the lever, the spring dynamometer was pulled vertically upward at a uniform speed, so that the spring dynamometer hanging under the lever OB

(1) The graduation value of the spring dynamometer is 0.1N, and the reading is: 2.5N;

(2) W is useful = Gh = 1.5N × 0.3m = 0.45 J;

W total=FS=2.5N×0.2m=0.5J;

η=W useful W total×100=0.45J0.5J×100=90

(3) Because the lever itself has gravity, when lifting the object, the lever must also be lifted, that is, overcoming the weight of the lever to do work, there will be extra work;

So the answer is: 2.5; 90; because When using a lever, you need to overcome the lever's own weight (overcoming friction) and other work.