F.3 PHYSICS
2010-05-31 3:42 am
john heat 1 kg of soup 25℃ to 70℃for 15mins with a heater. how long does it take to heat 1.5kg of the same kind of soup from 20℃to 80℃ with the same heater?
回答 (2)
2010-06-04 7:28 pm
✔ 最佳答案
First, you should calculate the 1. Let c and P be the specific heat capacity of soup and the power of heater respectively.
Pt=mc^T
(15)(60)( P)=(1)(c)(70-25)
so, 20P=c --------(1)
2. Let t (seconds) be the time required.
Pt=(1.5)(c)(80-20)
Pt=(1.5)(20P)(80-20) (from (1))
t=1800s
=30mins
2010-05-31 4:10 am
Heat supplied to heat 1 kg of soup from 25'C to 70'C
= 1 x C x (70-25) J = 45C J
where C is the specific heat capacity of the soup
Power delivered by the heater = 45C/15 J/min = 3C J/min
Heat needed to heat 1.5kg of soup from 20'C to 80'C
= 1.5C x (80-20) J = 90C J
Time required = 90C/3C minutes = 30 minutes
= 1 x C x (70-25) J = 45C J
where C is the specific heat capacity of the soup
Power delivered by the heater = 45C/15 J/min = 3C J/min
Heat needed to heat 1.5kg of soup from 20'C to 80'C
= 1.5C x (80-20) J = 90C J
Time required = 90C/3C minutes = 30 minutes
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