(20 14? Chengdu) Xiao Li and his classmates did an experiment to measure the mechanical efficiency of the pulley block: (1) They conducted the experiment in the order shown in the figure, where A.

(1) In the experimental operation, the spring dynamometer should be pulled up vertically at a uniform speed, so that the spring dynamometer is in a balanced state, and the pointer of the spring dynamometer reflects the magnitude of the pulling force;

(2) Mechanical efficiency of pulley block in Experiment C: η = w = w×100% = ghfs×100% =1.0n× 0.1m0.5n× 0.4m×1.

(3) By analyzing the experimental data of A and B, we can know that if the same pulley block is used twice, the heavier the hook code lifted the second time, the higher the mechanical efficiency, that is, the heavier the hook code lifted by the same pulley block, the higher the mechanical efficiency.

So the answer is: (1) uniform vertically; (2)50%; (3) The heavier it is.