How long will 700 kg of dry firewood be enough to heat one room, if a daily amount of heat equal to 250 MJ is spent on it?
The amount of heat that will be released during the complete combustion of firewood:
Q = q * m, where Q is the released amount of heat (Q = 250 MJ = 250 * 10 ^ 6 J), q is the specific heat of combustion of dry firewood (we take for dry firewood q = 1 * 10 ^ 7 J / kg), m is the mass of firewood for one day (kg).
m = Q / q = 250 * 10 ^ 6/10 ^ 7 = 25 kg.
The number of days for which 700 kg of dry firewood is enough (m1 = 700 kg):
N = m1 / m = 700/25 = 28 days.
Answer: 700 kg of dry firewood is enough for 28 days.
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