Question

Физика(КР) Прошу помочь(2 задачи) 78. На спиртовке нагрели m = 224 г воды от t1 = 15 °С до t2 = 75 °С и сожгли при этом m1 = 5 г спирта. Определите КПД спиртовки. 79. Велосипедный двигатель на s = 100 км пути при скорости u = 25 км/ч расходует m = 1 кг бензина. Определите мощность N двигателя, если его КПД η = 20 %.

Answer 1

Это лишнее......Ошибка вышла. Извините. У парня все верно

Answer 2

Из формул КПД и мощности через силу и скорость.

Answer 3

Problem 78: Efficiency of a Spirit Lamp

In this problem, we are given the mass of water (m = 224 g) and the initial and final temperatures (t1 = 15 °C and t2 = 75 °C) of the water. We are also given the mass of alcohol burned (m1 = 5 g). We need to determine the efficiency (η) of the spirit lamp.

To solve this problem, we can use the formula for efficiency:

η = (Q / Q1) * 100%

where Q is the heat absorbed by the water and Q1 is the heat produced by burning the alcohol.

To find Q, we can use the formula:

Q = m * c * ΔT

where m is the mass of water, c is the specific heat capacity of water, and ΔT is the change in temperature.

The specific heat capacity of water is approximately 4.18 J/g°C.

To find Q1, we can use the formula:

Q1 = m1 * ΔH

where m1 is the mass of alcohol burned and ΔH is the heat of combustion of alcohol.

The heat of combustion of alcohol varies depending on the type of alcohol. Let's assume we are using ethanol. The heat of combustion of ethanol is approximately 1360 kJ/kg.

Now, let's calculate the values and find the efficiency.

Given: - m = 224 g (mass of water) - t1 = 15 °C (initial temperature) - t2 = 75 °C (final temperature) - m1 = 5 g (mass of alcohol burned) - c = 4.18 J/g°C (specific heat capacity of water) - ΔH = 1360 kJ/kg (heat of combustion of ethanol)

Solution: 1. Calculate Q: - ΔT = t2 - t1 = 75 °C - 15 °C = 60 °C - Q = m * c * ΔT = 224 g * 4.18 J/g°C * 60 °C = 563,712 J

2. Calculate Q1: - Q1 = m1 * ΔH = 5 g * (1360 kJ/kg * 1000 J/kJ) = 6,800,000 J

3. Calculate efficiency: - η = (Q / Q1) * 100% = (563,712 J / 6,800,000 J) * 100% ≈ 8.29%

Therefore, the efficiency of the spirit lamp is approximately 8.29%.