Question

Мама поставила чайник на огонь, в чайнике было 5 литров воды мама ушла спать когда она проснулась в чайнике осталось 2 литра . сколько было дров в костре если КПД 12% на нагрев

Answer 1

Q отд = Q получ
m воды = 1000 * 0.005 = 5 кг
c воды = 4200 Дж / кг*С
q дров = 10 000 000 кг / Дж
L воды = 2 300 000 Дж / кг
Q отданное воде дровами = cmt + Lm =  4200 * 5 * 80 + 2 300 000 * 5 = 13 180 000 Дж.
КПД = 12%, значит полное выделение теплоты дровами = 13 180 000 : 0.12 = 109 833 333 Дж.
Q = qm = 109 833 333, отсюда m = Q/q = 109 833 333 / 10 000 000 = 11 кг.
Ответ: 11 кг

Answer 2

Calculation of the Number of Logs in the Fire

To calculate the number of logs in the fire, we need to know the efficiency of the heating process. The efficiency is given as 12%. This means that only 12% of the energy from the logs is used to heat the water in the kettle, while the remaining 88% is lost as waste heat.

Let's assume that the logs are the only source of heat for the kettle, and there is no heat loss from other sources. In this case, we can calculate the number of logs needed to heat the water from 2 liters to 5 liters.

To do this, we need to determine the amount of energy required to heat the water from 2 liters to 5 liters. The specific heat capacity of water is approximately 4.18 J/g°C. Since we know the volume of water and the temperature change, we can calculate the energy using the formula:

Energy = mass of water * specific heat capacity * temperature change

The mass of water can be calculated using the density of water, which is approximately 1 g/mL.

Let's calculate the mass of water:

Mass of water = volume of water * density of water

Substituting the values:

Mass of water = 3 liters * 1 g/mL = 3000 grams

Now, let's calculate the energy required to heat the water:

Energy = 3000 grams * 4.18 J/g°C * (100°C - 20°C) = 3000 grams * 4.18 J/g°C * 80°C = 1008000 J

Since the efficiency of the heating process is 12%, only 12% of the energy from the logs is used. Therefore, the total energy provided by the logs can be calculated as:

Total energy provided by the logs = Energy / Efficiency = 1008000 J / 0.12 = 8400000 J

Now, let's calculate the energy provided by each log. We need to convert the energy provided by the logs to joules per log. Assuming that each log provides the same amount of energy, we can divide the total energy by the number of logs:

Energy per log = Total energy provided by the logs / Number of logs

Substituting the values:

Energy per log = 8400000 J / Number of logs

Since we don't have the exact value for the energy per log, we cannot determine the exact number of logs in the fire.