Posted by Anonymous on .
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?

maths 
Steve,
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