List of top Agricultural Process Engineering Questions on Mechanics and energy requirement in size reduction

In a size reduction operation, the power required to crush 2 ton of feed material per hour is 7.2 kW. Eighty per cent of the feed and product material pass through 4.75 mm and 0.5 mm sieve openings, respectively. The work index of the material is:
Ball mill diameter = 200 cm. Ball sizes: 10 cm (dry), 20 cm (wet). Find change in operating speed (rpm) (round to 2 decimals). (Take π = 3.14, g = 9.81)