(1) During the experimental operation, the spring dynamometer should be pulled vertically upwards at a uniform speed. In this way, the spring dynamometer is in a balanced state, and the indication of the spring dynamometer reflects the magnitude of the pulling force.
Each large grid represents 1N, each small grid represents 0.2N, and the reading of the spring dynamometer is 2.4N.
W=Gh=6N×0.1m=0.6J
∵The weight is borne by 3 sections of rope,
∴S=3h=3×0.1 m=0.3m
∴W total=FS=2.4N×0.3m=0.72J
η=W useful W total×100=0.6J0.72J×100=83.3.
(2) The entire pulley block remains unchanged, that is, the additional work remains unchanged. Because the work done on the heavy object is useful work, reducing the number of hook codes means reducing the useful work, and the mechanical efficiency will decrease.
So the answer is:
(1) Uniform speed; 2.4; 0.6; 83.3 (or 83, 83.33). ?
(2) Reduce.