Name the main constituent of biogas.

Name the process responsible for large energy production in the sun?

Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.

Which type of process is currently used in nuclear electricity generation?

$(a)$ Describe the structure of a windmill.
$(b)$ Give one example to illustrate that energy from a windmill was used in the past to do mechanical work.

What type of energy is utilized by a sailing boat?