Engine displacement is the measure of the cylinder volume swept by all the pistons of a piston engine. The piston moves inside the cylinder bore. The cylinder bore in the form of circular cylinder open at the top is to be made from a metal sheet of area $75\pi \text{ cm}^2$. Based on the above information, answer the following questions : (i) If the radius of cylinder is r cm and height is h cm, then write the volume V of cylinder in terms of radius r. (ii) Find $\frac{dV}{dr}$. (iii) (a) Find the radius of cylinder when its volume is maximum. OR (b) For maximum volume, $h > r$. State true or false and justify.