F.3 Physics homework

Ka Lung

2010-10-23 2:45 am

14. An electric kettle can rise the temperature of 1 kg of water from 25 °C to
100 °C in 3 minutes.
(a) Find the energy absorbed by water. (2 marks)
(b) Find the effective output power of the electric kettle. (2 marks)
(Hints: Effective output power = __energy absorbed by water_
time

15. An immersion heater of power 120 W is used to heat 0.5 kg of a liquid for 70 s. The rise in the temperature of the liquid is 8 °C. Assume that there is no energy loss. Find the specific heat capacity of the liquid. (3 marks)

17.Consider a cup of 0.1 ~kg hot water at 60°C.
(a) If the hot water releases 8400 J of energy, what is the drop in the temperature of the water. (2 marks)
(b) If the hot water absorbs 6300 J of energy, what is the final temperature of the water? (2 marks)

注意:請盡可能詳細回答問題,包括公式及步驟!

回答 (1)

天同

2010-10-23 4:30 am

✔ 最佳答案

14(a) Energy absorbed = 1 x 4200 x (100-25) J = 315000 J(b) Output power = energy/time = 315000/(3x60) watts = 1750 watts
15. Energy delivered by the heater = 120 x 70 J = 8400 JHence, energy absorbed by the liquid = 8400 J
Specific heat capacity of liquid = 8400/(0.5x8) J/kg.C = 2100 J/kg.C
17.(a) Drop in temperature = 8400/(0.1 x 4200) 'C = 20'C(b) Rise in temperature = 6300/(0.1x4200) 'C = 15'CHence final temperature = (60 + 15)'C = 75'C

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