(1)m=ρ*V=1*1.5=1.5kg (ρ水=1kg/dm^3;1dm^3=1L)(2)Q吸=Cm(t2-t1)=4200*1.5*(100-20)=5.04*10^5J(3)P=Q/t=5.04*10^5/5*60=1680W(4)W电能=(240/1600)kwh=0.15kwh=0.15*3.6*10^6 (1kwh=3.6*10^6J)=5.4*10^5Jη=Q吸/W电能=5.04/5.4=93.33%