(2)∵ When not pulled, the pressure of the counterweight on the ground is f = g = 200 n;
∴ pressure on the ground p=FS=200N4× 10? 3 m2 = 5× 104 pa；
(3) useful work done by pulling force:
w = Gh = 200n×0.4m = 80J；
(4) The power of pulling force P = WT = 80J2S = 40W.
Answer: (1) The gravity on the counterweight is 200 N;
(2) When not pulled, the pressure of the counterweight on the ground is 5×104 Pa;
(3) During the pulling process, the work done by the pulling force on the counterweight is 80J；;
(4) In the process of traction, the traction power is 40W. ..