(1) F=1/2(200N + 2.98*10^4)=1.5*10^4 N
(2) W= F*S=F*2H=1.5*10^4 * 2 * 20 = 6*10^5 J
(3) 绳子速度V=P/F = 1.5*10^4/1.5*10^4N=1m/s,重物上升速度v=1/2 V = 0.5m/s
(4) η=2.98/3 * 100% = 97%
(1) F=1/2(200N + 2.98*10^4)=1.5*10^4 N
(2) W= F*S=F*2H=1.5*10^4 * 2 * 20 = 6*10^5 J
(3) 绳子速度V=P/F = 1.5*10^4/1.5*10^4N=1m/s,重物上升速度v=1/2 V = 0.5m/s
(4) η=2.98/3 * 100% = 97%