Q. 105.0( 1 Vote )

A body cools down from 65°C to 60°C in 5 minutes. It will cool down from 60°C to 55°C in
A. 5 minutes

B. less than 5 minutes

C. more than 5 minutes

D. less than or more than 5 minutes depending on whether its mass is more than or less than 1 kg.

Answer :

According to Newton’s Law of Cooling:

Here is the rate of fall of temperature is the constant depending on nature of surface and surrounding conditions, A is the area of cross-section of the body, T is the average Temperature of the body and T0 is the surrounding temperature.
It can also be written in Celsius scale as

Where θ and θ0 are the temperature of the body and surrounding in Celsius scale respectively , k is a constant.
First condition:
Temperature falls from 65° C to 60° C.
Which means 5°C falls in 5 minutes,

θ =
62.5 ° C
Substituting we get,

Second Condition:
Temperature further falls from 60 °C to 55 °C.
dθ= 5 °C.
θ =

Substituting value of -k,dθ and θ in the equation we get,

Here we can conclude that time required for the body to go from 60 ° C to 55° C will be,

Thus, option (c) is the correct option.

Rate this question :

How useful is this solution?
We strive to provide quality solutions. Please rate us to serve you better.
Related Videos
Work done in Thermodynamic ProcessWork done in Thermodynamic ProcessWork done in Thermodynamic Process43 mins
Try our Mini CourseMaster Important Topics in 7 DaysLearn from IITians, NITians, Doctors & Academic Experts
Dedicated counsellor for each student
24X7 Doubt Resolution
Daily Report Card
Detailed Performance Evaluation
view all courses