解：(1) m =ρV = 1.0 × 10 3 kg/m 3 × 10 -3 m 3 = 1kg, Q 吸 =cm( t - t 0 ) =4.2 × 10 3 J/( kg . ℃) ×1 kg × (100℃ -20 ℃) = 3. 36 × 10 5 J. (2) W =Pt =2 000 W ×200 s =4 ×10 5 J. =3.36 ×10 5 J/(4 ×10 5 J) =84%.
