Q. Water of volume $2\ litre$ in a container is heated with a coil of $1\ kW$ at $27℃.$ The lid of the container is open and energy dissipates at rate of $160\ J/s.$ In how much time temperature will rise from $27℃$ to $77℃$ [Given specific heat of water is $4.2\ kJ/kg$]
A) $8\min{20\ s}$
B) $6\min{2\ s}$
C) $7\ min$
D) $14\ min$
Explanation
(a) Heat gained by water = Heat supplied by container heat lost
$\Rightarrow mS\mathrm{\Delta}\theta = 1000t - 160t$
$\Rightarrow t = \frac{2 \times 4.2 \times 1000 \times 50}{840} = 8\min{20\ sec}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.