An immersion heater takes 5 minutes to raise 2 kg of water by 10 oC. If the same heater is used to raise 3 kg of water by 5 oC, how long will it take?
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Ans: 3.75 mins
點計?
physics question
2006-12-07 6:18 am
回答 (2)
2006-12-07 6:35 am
✔ 最佳答案
by E=mcΔTE=2c(10)=20c
P=E/T=20c/5=4c
by E=mcΔT
E=3c5=15c
P=E/T=15c/T
since the same heater, the power will be the same
15c/T=4c
T=3.75
2006-12-07 6:37 am
假設 heater 的功率是 X W 即 X J/s
5 分鐘共放出熱能 (X)(5)(60) = 300X
2 kg水升溫10oC 須吸入熱能 = mCΔT = (2)(4200)(10) = 84000 J
300X = 84000
X = 84000 / 300 = 280 J/s = 280 W
3 kg水升溫5oC 須吸入熱能 = mCΔT = (3)(4200)(5) = 63000 J
設須時 t 秒
63000 = 280t
t = 225 s = 3.75 分鐘
5 分鐘共放出熱能 (X)(5)(60) = 300X
2 kg水升溫10oC 須吸入熱能 = mCΔT = (2)(4200)(10) = 84000 J
300X = 84000
X = 84000 / 300 = 280 J/s = 280 W
3 kg水升溫5oC 須吸入熱能 = mCΔT = (3)(4200)(5) = 63000 J
設須時 t 秒
63000 = 280t
t = 225 s = 3.75 分鐘
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原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20061206000051KK04763