Question

сколько дров нужно сжечь,чтобы нагреть 5 кг воды от 20С до 100С? какую температуру будет иметь вода,если смешать 400 кг воды при 20С со 100 кг воды при 70С?

Answer 1

1) m"дров"·q"дров"=m"воды"c"воды"Δt

m"дров"= q"дров"/(m"воды"c"воды"Δt)≈7.7 кг. 

2) t=m₁t₁+m₂t₂/m₁+m₂

t=30⁰C 

Answer 2

Calculation of the amount of wood needed to heat 5 kg of water from 20°C to 100°C

To calculate the amount of wood needed to heat 5 kg of water from 20°C to 100°C, we need to consider the specific heat capacity of water and the energy required to raise its temperature.

The specific heat capacity of water is approximately 4.18 J/g°C. This means that it takes 4.18 Joules of energy to raise the temperature of 1 gram of water by 1 degree Celsius.

Given that we have 5 kg of water (which is equivalent to 5000 grams), we can calculate the energy required to heat it from 20°C to 100°C using the formula:

Energy = mass × specific heat capacity × temperature change

Temperature change = final temperature - initial temperature = 100°C - 20°C = 80°C

Energy = 5000 g × 4.18 J/g°C × 80°C = 1672000 J

Now, let's convert the energy into a more practical unit, such as kilocalories (kcal). 1 kilocalorie is equal to 4184 Joules.

Energy in kilocalories = 1672000 J / 4184 J/kcal = 399.42 kcal

Therefore, approximately 399.42 kilocalories of energy would be required to heat 5 kg of water from 20°C to 100°C.

Please note that this calculation assumes 100% efficiency in converting the energy from burning wood into heating the water. In reality, there will be some energy losses due to factors such as heat dissipation.