Question

A piece of metal is heated to 428 degree C before it is left to cool. The temperature of the metal falls at the rate of 23 degree C per minute for first three minutes, at the rate of 15 degree C per minute for the next 15 minutes and then at the rate of 8 degree C per minute until it reaches to room temperature of 25 degree C from 428 degree C i. Find Temperature of the metal after 9 minutes. ii. The total time needed for the metal to reach a temperature of 25 degree C from 428 degree C.

Answer 1

i). 269° C

ii). 31m 37.5sec

Step-by-step explanation:

Given that,

The Temperature drops = 23°C per minute

The temperature dropped in 3 minutes = 23*3 or 69°C  

i). Temperature of the metal after 9 minutes = 428°-159° = 269° C

ii). The total time needed for the metal to reach a temperature of 25° C from 428° C

= '3 minutes = drop 69°C.

In 15 minutes = drops 225° C.

Now, 134° C is left as temperature after 18 minutes.'

'It is 109° C above 25° C, and it falls 8° C a minute or 109/8 = 13 (5/8) minutes more.'

This requires 31 (5/8) minutes or 31m37.5s

Learn more: find the required temperature

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