An alloyed fiat disk weighs 19.9 g. The disk having diametre 31.2 mm has a hole of 7.6 mm diametre. If the thickness of diametre is 4. 6 mm, calculate the density of the alloy.

h=4.6mm,r1=31.2/2=15.6mm;r2=7.6/2=3.8mm.∴ V=πhr12−r22=3.14×4.6mm(15.6mm)2−(3.8mm)2=3.14×4.6mm243.36mm2−14.44mm2=3.14×4.6mm×228.92mm2=3306mm3=3.306cm3∵ 1mm3=10−3cm3Also,  Density = Mass  Volume =19.9g3.306cm3=6.02gcm−3=6.02×103kgm−3=6020kgm−3