[急]F.4 Phy

水的質量，mw = 2 kg

水的比熱容量，cw = 4200 Jkg-1℃-1

水的溫度改變，△Tw = 40 – 37 = 3℃

所以，溫水失去的能量，Ew

= mwcw△Tw

= 2 X 4200 X 3

= 25 200 J

設沒有能量損失

根據能量守恆定律

冰吸收的能量 = 水失去的能量

設冰的比潛熱為L

冰的質量，m = 0.06 kg

冷水的溫度改變，△T = 37℃

所以，mL + mcw△T = Ew

0.06L + 0.06 X 4200 X 37 = 25 200

L = 2.65 X 105 Jkg-1

By conservation of energy,

heat lost by the 40'C 熱水 = heat gained by the ice

mc(T - T*) = m' L + m'c'(T' - T*)

2 x 4 200 x (40 - 37) = 0.06 x L + 0.06 x 4 200 x (37 - 0)

25 200 = 0.06L + 9 324

0.06L = 15 876

L = 264 600 J/kg