What length of a solid cylinder 2cm in diameter must be taken to recast into hollow cylinder of length 16cm,external diameter 2cm and thickness 2.5mm?

Answer 1

for the hollow cylinder,

outside volume is pi * 1^2 * 16 = 16pi
inside volume = pi * (1-.25)^2 * 16 = 9pi

volume of metal = 7pi cm^3

volume of solid is thus

7pi = pi * 1^2 * h = h*pi
h = 7 cm

Answer 2

What length of solid cylinder 2 cm in diameter must be taken to recast into a hollow cylinder of length 16 cm x 10 external diameter 20 cm and thickness 2.5 mm