(a) Define mechanical power and state its SI unit.
(b) A body is pulled along a straight, horizontal surface by a constant force F and moves with a uniform velocity v. Starting only from the definition of power as the rate of doing work, derive an expression that relates P, F and v.
(c) Mention one practical situation in everyday life where the expression obtained in part (b) is more convenient to use than the basic definition P=W/t.