Useful facts specific heat of stone, 800 J/(kg K) specific heat of water, 4186 J

Question

Useful facts specific heat of stone, 800 J/(kg K) specific heat of water, 4186 J/(kg K) latent heat of vaporization of water, 2.26 x 10 J/kg Hot stone cooking In a volcanic area, water in a pan may be brought to a tossing At a camp, stones each with in enough hot stones. a mass of 0.48 kg and a of 155 are tossed in a large pan The by means of an insulating tool, one stone at a time. pan contains 1.4 kg of water initially at 21° and a glass-bulb thermometer to check progress toward boil. a few minutes, been the After twelve stones have added but water is still not boiling. us neglect heat exchanges w surrounding air. Answer parts (a) and (b) in the devoted spaces. Show all your steps clearly, commenting as needed (a) What is the current reading of the water thermometer

Explanation / Answer

Mass of each stone, ms = 0.48 kg
Temperature of stone , Ti = 155 oC
Mass of water , mw = 1.4 kg
Temperature of water , Tw = 21 oC

(a)
Let the current reading be Tf

Heat Lost by Stone = Heat gained
mw * Cw * T = ms * Cs * T
1.4 * 4186 * (Tf - 21) = 12 * 0.48 * 800 * (155 - Tf)
Tf = 79.98 C
Temperature of the thermometer , Tf = 80 oC

(b)
Boiling point of
To reach boiling point of water stone needed be x.
mw * Cw * T + mw * Lv = ms * Cs * T
1.4 * 4186 * (100 - 21) + 1.4 * 2.26 * 10^6 = x * 0.48 * 800 * (155 - 100)
x = 171.7

No of more stones needed = 172 - 12 = 160

P.S :-
The above was the case when the water starts boiling, if they are looking for point we just reach 100 oC, then answer would be :- 22 - 12 = 10 stones

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