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?
2006-12-06 17:18:08 · 2 個解答 · 發問者 bubibubi 2 in 科學 ➔ 其他：科學
by E=mcΔT
E=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
2006-12-06 17:35:46 · answer #1 · answered by HIM 2 · 0⤊ 0⤋
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
2006-12-06 17:37:17 · answer #2 · answered by ? 7 · 0⤊ 0⤋