Question

В чайник сопротивлением 5_ Ом налили з кг и включили в сеть с напряжением 220 вольт. Определите начальную температуру воды если через 2 мин вода закипела. Теплопотерями пренебречь. Удельная теплоёмкость воды 4200 Дж/кгС

Answer 1

Дано:

R=5 Ом

m=3 кг

U=220 В

T=2 мин=120 с

tк=100°C

c=4200 Дж/кг×C

tн-?

Решение:

$Q = \frac{U^{2} }{R}T = \frac{220^{2} }{5} \times 120 = 1161600 Дж$

Q=cm(tк-tн)

Пусть tн=x, тогда cm(tк-x)=Q

4200×3(100-x)=1161600

12600(100-x)=1161600

1260000-12600x=1161600

-12600x=1161600-1260000

-12600x=-98400

x=-98400/-12600

x≈7,8

Ответ:tн=7,8 °C.

Answer 2

Calculating Initial Water Temperature

To calculate the initial temperature of the water in the kettle, we can use the formula for the heat energy required to raise the temperature of the water from the initial temperature to the boiling point. The formula is:

Q = m * c * ΔT

Where: - Q = heat energy - m = mass of the water (in kg) - c = specific heat capacity of water (in J/kg°C) - ΔT = change in temperature (in °C)

We can rearrange the formula to solve for the initial temperature (T_initial):

T_initial = T_boiling - (Q / (m * c))

Where: - T_boiling = boiling point of water (100°C)

Calculation Steps

1. Calculate the heat energy required to raise the temperature of the water to the boiling point using the formula Q = m * c * ΔT. 2. Use the calculated heat energy to find the initial temperature using the formula T_initial = T_boiling - (Q / (m * c)).

Calculation

Given: - Resistance of the kettle, R = 5 Ω - Voltage, V = 220 V - Time, t = 2 minutes = 120 seconds - Specific heat capacity of water, c = 4200 J/kg°C - Boiling point of water, T_boiling = 100°C

We can calculate the heat energy using the formula Q = V^2 * t / R:

Q = (220^2 * 120) / 5

Now, we can use the calculated heat energy to find the initial temperature:

T_initial = 100 - (Q / (m * c))

Conclusion

Using the given values and the calculations, we can determine the initial temperature of the water in the kettle.