Question

A beaker full of hot water is kept in a room. If it cools from 80°C to 75°C in t1 minutes, from 75°C to 70°C in t2 minutes and from 70°C to 65°C in t3 minutes, then ___________

(a) t1=t2=t3

(b) t1 < t2 = t3

(c) t1 < t2 < t3

(d) t1 > t2 > t3

This question was posed to me during an internship interview.

This interesting question is from Temperature and Specific Heat in chapter Mechanical Properties of Solids of Engineering Physics I

Answer 1

The correct answer is (c) t1 < t2 < t3

To elaborate: According to Newton’s law of cooling, Rate of cooling is proportional to temperature difference of the body and its surroundings.

As the temperature of the body approaches the room temperature, rate of cooling decreases.

t1 < t2 < t3.