Question

A composite disc is to be made using equal masses of aluminium and iron so that it has as high a moment of inertia as possible. This is possible when:

• A. The surfaces of the disc are made of iron with aluminium inside
• B. The whole of aluminium is kept in the core and the iron at the outer rim of the disc
• C. The whole of the iron is kept in the core and the aluminium at the outer rim of the disc
• D. The whole disc is made with thin alternate sheets of iron and aluminium

Answer 1

The correct option is B The whole of aluminium is kept in the core and the iron at the outer rim of the disc

Density of iron $>$ Density of aluminium
Moment of inertia = $\int r^{2}dm$
$\therefore$ Since ${\rho }_{iron}>{\rho }_{aluminium}$
So whole of aluminium is kept in the core and the iron at the outer rim of the disc.