A typical grinding wheel is 9 in. in diameter, 1 in. thick, and weighs 6 lb. The wheel contains SiC (density of 3.2 g/cm3 ) bonded by a silica glass (density of 2.5 g/cm3 ); 5 vol% of the wheel is porous. The SiC is in the form of 0.04 cm cubes. Calculate (a) the volume fraction of SiC particles in the wheel and (b) the number of SiC particles lost from the wheel after it is worn to a diameter of 8 in.