posted by Anonymous .
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?
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