Simple Physics question about rotational inertia

AI Thread Summary
The discussion revolves around calculating the mass and rotational inertia of a child's bowling ball compared to an adult's. The child's ball has two-thirds the radius of the adult ball, leading to a mass reduction factor of 1/3. For rotational inertia, the calculation involves the formula 1/2 MR^2, resulting in a reduction factor of 1/3 as well. Participants clarify the need for the volume of a sphere formula to support their calculations. The conversation emphasizes understanding the relationship between radius, mass, and rotational inertia in spherical objects.
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Homework Statement


A bowling ball made for a child has two thirds the radius of an adult bowling ball. They are made of the same material (and therefore have the same mass per unit volume).
(a) By what factor is the mass of the child's ball reduced compared with the adult ball?

(b) By what factor is the rotational inertia of the child's ball reduced compared with the adult ball?


Homework Equations



1/2 MR^2 , i believe

The Attempt at a Solution


I thought that the answer to part is is just 1/3 but my online assignment is accepting it as the correct answer.
part b would then be 2/3 squared * 1/2 = 1/3
 
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(a) What is the formula for the volume of a sphere?
 

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