a) Re=R1+R2=2+5=7Ω=>Re=7 Ω
b)E=I*Re+Ir<=>E=I(Re+r)<=>60=I(7+3)<=>60=10I=>I=6 A
c)P1=R1*I^2=2*6^2=2*36=72 W=>P1=72W
d)t=5 min=300 s
W1=U1*I*t=R1*I^2*t=2*6^2*300=600*36=21600 J=>W1=21600 J
e)η=Re/(Re+r)=7/(7+3)=7/10=0,7=>η=70%
f)P=E*I=60*6=360 W=>P=360 W
