A cube of metal side is 7cm melted down and recast in a cylindrical mould with a diameter of 3cm. How long is the cylinder of metal?

The volume of the cube = (7cm)^3 = 343cm^3

Therefore, the cylinder has the same volume (assuming no loss due to melting)...so we have

343 = pi*r^2 *h →

343 =pi*(1.5)^2*h →

343 / [pi *(1.5)^2] = h = about 48.52cm