Question

You have two identical looking spools (same mass, same shape, same size). However, one is hollow, made from iron, the other is solid, made from aluminum. A string is wound around each spool. If you pull on both strings with equal forces, which spool is going to have the larger angular acceleration

Answer 1

The one made from AL will have a smaller moment of inertia and thus a greater acceleration:

α = I ω

I = M R^2 for the iron (all the mass at a distance R)

Replacing any of the Fe with Al (and putting at a smaller radius) is going to reduce the total moment of inertia,