Question

A body is heated to temperature 40 degree and kept in a chamber maintained at 20⁰. If temperature decreases to 36⁰ in 2 minutes. Time after it will further decrease by 4 degree is -

• A. 2 min
• B. 2 min 33 sec
• C. 2 min 55 sec
• D. 3 min

Answer 1

Answer: (B)

2 min 33 sec

Answer 2

$\frac{d\theta}{dt}$ = – k (q – q₀)

From 40⁰ to 36⁰ : q = $\frac{40 + 36}{2}$ = 38

$\frac{d\theta}{dt}$ = $\frac{4}{2}$ = 2 degree/min

From 36⁰ to 32⁰ : q = 14

$\frac{d\theta}{dt}$ = $\frac{4}{t}$

Ž $\frac{4/2}{4/t}$ = $\frac{38}{34}$

Ž t = 2 min 33 sec