(1) Because the same two bags of sand are hoisted from the ground on the first floor to the ground on the second floor with pulleys A and B respectively, the objects have the same gravity and the same hoisting height, according to the formula W=Gh, the useful work of the two cases is the same; W useful 1=W useful 2.

(2) When the useful work is constant, the total work done by A is the work done on a bag of sand. The less extra work you do when using the machine, the less total work you do. Because the useful work is the same, the higher the mechanical efficiency. Because B is a moving pulley, the total work done by B should be added to the work done by the moving pulley. The more extra work done by pulley B, the more total work, and the lower the mechanical efficiency. That is, w is 1 < W is 2, η 1 > η 2,

So the answer is: