SOLUTION: 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 t

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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).
Please help to solve this question.
I have tried to calculate the volume of the sphere using the internal radius but then I'm stucked with what I needed to do with the external radius ?
Thank you very much.
Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
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.