$A$ person holds a bundle of hay over his head for $30$ minutes and gets tired. Has he done some work or not? Justify your answer.

(N/A) In scientific terms,the person has done no work.
Work is defined as the product of the force applied and the displacement in the direction of the force $(W = F \times s)$.
Since the bundle of hay is held stationary over the head,the displacement $(s)$ is $0$.
Therefore,$W = F \times 0 = 0$.
The person feels tired because his muscular energy is being consumed and converted into thermal energy to maintain the posture,but this does not constitute mechanical work.