(1) The index of the spring dynamometer is 3N+0.2N=3.2N, so the pulling force f = 3.2n

The rising height of the spring dynamometer: s = 45.0cm-25.0cm = 20.0cm = 0.2m；;

Work done by pulling force: w sum = fs = 3.2n×0.2m = 0.64j；;

(2) The rising distance of the object H =10.0cm-0.0cm =10.0cm = 0.1m,

w has = mgh = 0.5kg× 10n/kg×0. 1m = 0.5j，

Mechanical efficiency of moving pulley:

η=W, w total ×100% = 0.5j0.64j×100% ≈ 78.1%.

Answer: (1) The work done by the tension F of the spring dynamometer on the rope is 0.64 J;

(2) The mechanical efficiency of this pulley block is 78. 1%.