r10=35.;
r50=10.;
g10=1/r10;
g50=1/r50;
Solve[{a*10+b==g10,a*50+b==g50}]

gamma=Fit[{{10,g10},{50,g50}},{1,T[t]},T[t]]

a=0.1;
b=0.1;
c=0.1;
ρ=1000;
objem=a*b*c;
m=objem*ρ;
Print["m= ",m," kg"]
U=230;
vykon=(U^2)*((gamma*b*c)/a);
cp=4186;
rce=m*cp*T'[t]==vykon
res=DSolve[{rce,T[0]==4},T[t],t][[1]]
tmax=10;
Plot[T[t]/.res,{t,0,1000},AxesLabel->{"t[s]","T[°C]"},PlotStyle->{Red,Thick}]

gammaX=gamma/.t->x
(*gammaX=Fit[{{20,(1/72)},{75,(1/30)}},{1,T[x]},T[x]]*)

QV=1*(10^(-3));
mm=0.001;
d=3mm;
e=0.2;
vx=(QV/(e*d));
Ecko=(U/d);
rce=ρ*cp*vx*T'[x]==(Ecko^2)*gammaX;
res=DSolve[{rce,T[0]==4},T[x],x][[1]]
tmax=10;
Plot[T[x]/.res,{x,0,1.2},AxesLabel->{"t[s]","T[°C]"},PlotStyle->{Red,Thick}]

T2=(T[x]/.res)/.x->1.2
ρ*QV*cp*(T2-4);
Print["vykon je  ",((%)/1000),"  kW"]