Question

A body cools from 72°C to 68°C in 1 minute and from 62°C to 580C in 1.25 minute and from θ°C to 38°C in 2.5 minute. The surroundings is at a constant temperature of θ°C . Then

(1) θ₀ = 20 θ = 42

(2) θ₀ = 20 θ = 40

(3) θ₀ = 18 θ = 44

(4) θ₀ = 20 θ = 43

Answer 1

(2) θ₀ = 20 θ = 40

Let m amd c be mass and specific heat of body. Then

where k is a constant of proportionality. Similarly

From Eqns. (1) and (2) we have

When body cools from θ°0 to 380C in 2.5 minute;

From Eqns. (1) and (3) we have