Energy changes ：練習問題

Which of the following objects possesses kinetic energy?

A student consumes a snack providing \(150\text{ kcal}\) of chemical energy. If the energy conversion efficiency of their muscles for performing work is \(20\%\), how much useful work in Joules (\(J\)) can be performed? (Assume \(1\text{ kcal} = 4200\text{ J}\))

In a model steam engine connected to a small generator, what is the correct sequence of energy conversions occurring to produce useful electrical energy from the fuel?

In the process of photosynthesis, green plants convert light energy into which form of stored energy?

Green plants carry out photosynthesis to produce food. Which energy conversion correctly describes this process?

Besides the Joule (\(J\)), name the other unit of energy mentioned in the syllabus that is commonly used to measure the energy content of food.

A specific food sample contains \(25\text{ kcal}\) of chemical energy. Given that \(1\text{ kcal} = 4.2\text{ kJ}\), calculate the energy content of the food in Joules (J).

A specific energy converter system is composed of two stages. In the first stage, chemical energy is converted to kinetic energy with an efficiency of \(30\%\). The entire kinetic energy output from the first stage is then used as the input for a second stage, which converts it into electrical energy with an efficiency of \(20\%\). Calculate the overall energy conversion efficiency of this two-stage system and the total electrical energy output if the initial chemical energy input is \(5000\text{ J}\).

An electric kettle is a common household appliance used to boil water. It is powered by electricity from a wall socket.

a) Identify the form of energy supplied to the kettle and the primary useful form of energy it is converted into for heating the water. (2 points)

b) State the full name of the standard unit used to measure energy in the International System of Units (SI). (1 point)

c) According to the Law of Conservation of Energy, can energy be created or destroyed during the boiling process? (1 point)

A student uses a small model steam engine that burns fuel to turn a wheel.
(a) Describe the sequence of energy conversions, starting from the fuel until the wheel turns. (2 points)
(b) The engine is supplied with \(5000\text{ J}\) of chemical energy. If the engine has an efficiency of \(12\%\), calculate the amount of useful kinetic energy produced. (1 point)
(c) According to the Law of Conservation of Energy, if \(4400\text{ J}\) of energy is wasted as heat, and the rest is wasted as sound, calculate the amount of sound energy produced. (2 points)