(1)桩锤对桩的压强是P=
=
=5×10 4Pa;
(2)卷扬机克服重力做的功W 有=mgh=400kg×10N/Kg×1.8m=7.2×10 3J,
卷扬机的效率是η=
×100%=60%,解得,P=6000W.