... 5Ar=4000 => Ar= 400 =80 0J => 10.mr.h = 80 0 => mr=8kg 2.Lc ma sỏt hiu sut ca c h 0.25 Cụng ton phn dựng kộo vt: Atp=F2.l =1900.12=2 280 0J Cụng hao phớ ma sỏt: Ahp=Atp A1 =2 280 0-20000= 280 0J Vy lc ma ... ln v lc thỡ li thit by nhiờu ln v ng i, nờn nõng vt on h thỡ kộo dõy mt on s = 2h Do ú 0.25 cụng phi dựng l: 0.25 Atp=F1.s=F1.2h=1200.2.10 = 24000J Ai Hiu sut ca h thng l: H = A = 83 ,33% 0.25 1b ... ma sỏt: Ahp=Atp A1 =2 280 0-20000= 280 0J Vy lc ma sỏt: Fms= A'hp 280 0 = = 233,33N 12 l Hiu sut ca mt phng nghiờng: H2= A1 100% =87 ,72% A'tp 0.25 0.25 0.25 - Gi m1, V1, D1 ,l lng, th tớch v lng...