Phy Heat question

2009-03-14 10:19 pm

Iron blocks,A and B,are heated by heaters C and D respectively for the same period of time.The ratio of the power of C to that of D is 3:4.If the ratio of the temperature change of A to that of B is 4:3,what is the ratio of the mass of A to that of B?

Thx...

回答 (1)

天同

2009-03-14 10:42 pm

✔ 最佳答案

Let powers of heaters C and D be 3k and 4k respectively, where k is a proportional constant
and the temperature changes of blocks A and B be 4t and 3t respectively, where t is a proportional constant.
For block A,
3k = (Ma).c.(4t)
where Ma is the mass of block A and c is the specific heat capacity of iron
For block B,
4k = (Mb).c.(3t)
where Mb is the mass of block B
Dividing, 3k/4k = (Ma/Mb).(4t/3t)
i.e. Ma/Mb = (3/4).(3/4) = 9/16

2009-03-14 14:46:12 補充：
Sorry...I have missed out the time of heating. The left hand side of both equations should be multiplied by the heating time, but this would be cancelled out in dividing as the heating times are the same.

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