$(a)$ 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.

(N/A) windmill consists of a large structure erected at a significant height on a rigid support. At the top,it features blades similar to a fan. To generate electricity,the rotational motion of the windmill is utilized to turn the turbine of an electric generator.
$(b)$ $A$ water-lifting pump is a classic example where the rotational motion of a windmill was historically used to lift water from wells for irrigation or domestic use.