Question

A carpet cleaning machine holds 40litres of water. It is filled with water at 15 ∘ C and the water is heated by a 3.0kW element to a temperature of 70 ∘C.
How much energy is added to the water?
Mass of 1.0litre=1.0kg; s.h.c.=4200J/(kgK)]

Answer 1

The enegy transfered to the water is given by the following expression:

$$Q = cm(T_2 - T_1)$$

where $c = 4200J/(kg\cdot K)$ is the s.h.c. of water, $m = 40kg$ is the mass of the water, $T_1 = 15\degree C = 288K$ is the initial temperature of the water and $T_2 = 70\degree C = 343K$ is the final temperature of the water. Finally, obtain:

$$Q = 4200\cdot 40\cdot (343-288) = 9240000J = 9.24\times10^6J = 9.24MJ$$

Answer. 9.24*10^6 J or 9.24 MJ.