Question

A body cools from 91oC to 89oC in 5 minutes when the room temperature is 20oC. Then it will cool from 71oC to 69oC in:   

Solution

Correct option is

7 minutes

 

Room temperature = 20oC. 

In the first interval of 5 minutes:   

Mean temperature =    

Mean temperature excess = 90 – 20 = 70oC  

Average rate of loss of heat   

                 

Now, average rate of loss of heat ∝ mean temperature excess

         

Let t be the time taken to cool from 71oC to 69oC.

Then, for the second stage:

   

Mean temperature excess = 70 – 20 = 50oC.   

Average rate of loss of heat   

Dividing eq. (1) by (2),

                   

SIMILAR QUESTIONS

Q1

Mercury thermometers can be used to measure temperatures up to:

Q2

Which of the following is the smallest temperature?

Q3

The temperature at which the reading of a Fahrenheit thermometer will be double that of Centigrade thermometer is:

Q4

In a resistance thermometer the resistances at 0oC and 100oC are 6.74 and 7.74 ohm respectively. The temperature corresponding to 6.53 ohm resistance is:   

Q5

Which of the following has the highest specific heat? 

Q6

Which of the following has the highest specific heat? 

Q7

A liquid is being converted into vapours at its bp; the specific heat of liquid at this temperature will be:

Q8

Specific heat of a gas undergoing adiabatic change is:

Q9

Which of the following produces more servere burns? 

Q10

Three liquids with masses m1m2m3 are thoroughly mixed. If their specific heats are s1s2s3 and their temperature θ1θ2θ3 respectively, then the temperature of the mixture is: