physics - heat questions

2010-03-21 11:22 pm

1) john is using a 200-W electric heater to heat 0.h5 kg of soup.Wt is the tempature of the soup after 5 mins if its initial temperature is 20C?Assume all the energy given out by the heater is absorbed by the soup.(Specific heat capacity of the soup = 300J kg^-1 C^-1)

2) A 3kg metal block is heated to 100C and then put into a 5kg water bath.The temperature of the water bath rises from 27C to 31.7 C.What are the specific heat capacity and heat capacity of the metal block?( Specific heat capacity of water=4200)

please help!

更新1:

in question 1 , it should be o.5 kg instead of 0.h5 kg:) and the specific heat capacity should be 3500! thankyou !

回答 (1)

天同

2010-03-22 12:09 am

✔ 最佳答案

1. "...0.h5 kg of soup..", there must be a typo !

Heat given out by the heater in 5 minutes
= 200 x 5 x 60 J = 60 000 J

Change in temperature of soup = 60000/(m x 300) 'C
where m is the given mass of soup

Final temperature of soup =[ 60000/(m x 300) + 20]'C
[Note; I don't think the specific heat capacity of 300 J/kg-C for the soup is a realistic value. Try to check if the given figure is correct].

2. Let C be the heat capacity of the metal block
Heat absorbed by water = 5 x 4200 x (31.7 - 27) J = 98700 J
Heat given out by metal block = C.(100-31.7) J = 68.3C J

Hence, 98700 = 68.3C
i.e. C = 1445 J/kg

Specific heat capacity of metal block = 1445/3 J/kg-C = 482 J/kg-C

2010-03-21 22:05:17 補充：
Just substitute 0.5 kg into m, and use the correct value of 3500 J/kg-C for the specific heat capacity. I think you could calculate the result yourself.

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