How many kg of dry firewood need to be burned in order to heat 10 kg of water from 30 degrees C to boiling.

How many kg of dry firewood need to be burned in order to heat 10 kg of water from 30 degrees C to boiling. The answer must be rounded to hundredths. The specific heat capacity of water is 4200 J / (kg. C), the specific heat of firewood is 13 x 10 in 6 J / kg.

Condition:
m water = 10
t1 = 30 ° C
t2 = 100 ° C
c = 4200 J / (kg.gr. ° C)
q = 13 х10 ^ 6 J / kg
To find :
m firewood -?
Q combustion of wood-Q heating water = 0
q * m firewood = c * m water * Δt
m firewood = c * m water * Δt / q
m firewood = c * m water * (t1-t2) / q
m firewood = 4200 * 10 * 70/13 * 10 ^ 6 = 0.23
Answer: 0.23.