Question 40803
A hollow metal sphere has an internal radius of 20 cm and an external radius of 30 cm.  Given that the density of the metal is 7.8 g/cm^3 (gramme per cm cube), find the weight of the sphere. (Take PI to be 3.14).

V=(4/3)(pi)r^3
Volume of the shell = Volume of 30cm sphere - Vol of 20cm sphere
Vol(shell)=(4/3)(pi)[30^3-20^3]
          =(4/3)(3.14)(27000-8000)
          =(4/3)(3.14)(19000)
          =79546 cm^3
Weight = 7.8(79546)=148200 grams
Cheers,
Stan H.