Solution:
Given height of the cylinder, h = 2.5 mm = 0.25 cm
Radius of the cylinder, r = 12 cm
Volume of the cylinder = r2h
= ×122×0.25
= ×144×0.25
= 36 cm3
Let R be the radius of the sphere.
Volume of sphere = (4/3)R3
Since metallic disc is melted and made into a sphere, their volumes remains same.
(4/3)R3 = 36
R3 = 36×3/4
R3 = 27
Taking cube root
R = 3 cm
Hence the radius of the sphere is 3 cm.