Question

If the farmer were to use dry firewood with an average energy density of 16 MJ/kg, how many kilograms of wood would the farmer need to use to raise the water in the drum by the same amount as in (b)?

4.375 kg
5.625 kg
6.875 kg
7.125 kg

Answer 1

The farmer would need to use 1.25 kg of wood to raise the water in the drum by the same amount.

Step-by-step explanation:

To raise the water in the drum by the same amount as in the previous question, we need to calculate the amount of energy required to heat the water. The drum is filled with 1,000 kg of water and has a specific heat capacity of 4,000 J/kg/°C. Assuming a 5 degree change in temperature, we can calculate the total energy required as follows:

Total energy = specific heat capacity * mass * temperature change = 4,000 J/kg/°C * 1,000 kg * 5 °C = 20,000,000 J = 20 MJ

Now, we can calculate the mass of dry firewood needed with an average energy density of 16 MJ/kg:

Mass = total energy / energy density = 20 MJ / 16 MJ/kg = 1.25 kg

Therefore, the farmer would need to use 1.25 kg of wood to raise the water in the drum by the same amount.