w total = FS = f×3h = 200n×3×0.5m = 300j，

(2) Work done to overcome the gravity of an object:

W useful = GH = mgh = 30kg×10n/kg× 0.5m =150j,

Mechanical efficiency of pulley block;

η=w Useful w Total ×100% =150J300J×100% = 50%.

So the answer is: 300; 50%.