Diameter of the solid cylinder = 2 cm

 

Length of hollow cylinder = 16 cm

 

The solid cylinder is recast into a hollow cylinder of length 16 cm, external diameter of 20 cm and thickness of 2.5 mm = 0.25 cm

 

We know that,

 

Volume of a cylinder = πr2h

 

Radius of the solid cylinder = 1 cm

 

So,

 

Volume of the solid cylinder = π12h = πh cm3

 

Let’s assume the length of the solid cylinder as h

 

And,

 

Volume of the hollow cylinder = πh(R2– r2)

 

Thickness of the cylinder = (R – r)

 

0.25 = 10 – r

 

So, the internal radius of the cylinder is 9.75 cm

 

Volume of the hollow cylinder = π × 16 (100 – 95.0625)

 

Hence, it’s understood that

 

Volume of the solid cylinder = volume of the hollow cylinder

 

πh = π × 16(100 – 95.06)

 

h = 79.04 cm

 

Therefore, the length of the solid cylinder is 79.04 cm.