Solution: (1) from g = mg =140 *10n =1400n. According to Newton's third law, the pressure of counterweight A on the ground is1400 n. (2) Integration method: If the pulley weight is m, then (m+M)g*h=340J can be brought into the data to get M=30kg. (3) The counterweight A is equal to the pressure of people on the ground and the pressure of F =p*s is equal, and F 1 (lever left pull) =2F2 (lever right pull). According to Newton's third law and the lever is in a horizontal position, (m people g-f2)/s1= (m+m) g-2 *.