Question

Some plastic balls of radius 1 cm were melted and cast into a tube. The thickness, length and outer radius of the tube were 2 cm, 90 cm and 30 cm respectively. 

How many balls were melted to make the tube? 

Given: For the cylindrical tube, 

height (h) = 90 cm, 

outer radius (R) = 30 cm, 

thickness = 2 cm 

For the plastic spherical ball, 

radius (r₁) = 1 cm 

To find: Number of balls melted.

Answer 1

Inner radius of tube (r) 

= outer radius – thickness of tube 

= 30 – 2 

= 28 cm

Volume of plastic required for the tube = Outer volume of tube – Inner volume of hollow tube

∴ 7830 plastic balls were melted to make the tube.