13.
v=90 m/min=1,5 m/s
P=12 kW=12000 W
P=F*v=>F=P/v=12000/1.5=8000 N
F=G=mg=>m=F/g=8000/9,8=816,32 kg
16.
Rs₁=R₂+R₃=20+30=50 Ω
Rp₁=Rs₁*R₄/(Rs₁+R₄)=50*50/(50+50)=2500/100=25 Ω
Rs₂=R₁+Rp₁=15+25=40 Ω
Rp₂=R₆R₇/(R₆+R₇)=70*30/(70+30)=2100/100=21 Ω
Rs₃=R₅+Rp₂=39+21=60 Ω
Re=Rs₂Rs₃/(Rs₂+Rs₃)=40*60/(40+60)=2400/100=24 Ω
