The problem involves calculating the moment of inertia of a hollow sphere with given mass and radii. The original poster attempts to apply the formula for a hollow sphere but arrives at an incorrect result, prompting a request for assistance.
Some participants have offered guidance on alternative approaches to the problem, while others express confusion about the definitions and calculations involved. There is a mix of interpretations regarding the correct method to use for the hollow sphere's moment of inertia.
Participants note the need to compute the density of the material and clarify the distinction between a hollow sphere and a spherical shell, which may affect the calculations. There is an emphasis on understanding the mass distribution in relation to the moment of inertia.
George3 said:Homework Statement
A hollow sphere has a mass of 15 kg, an inner radius of 12 cm and an outer radius of 18 cm. What is the rotational inertia (moment of inertia) of the sphere about an axis passing through its center?
Homework Equations
The Attempt at a Solution
I = 2/3 MR^2 for a hollow sphere so i did this:
2/3 (15) (.18^2) = .32 kg m^2
But this is wrong the answer is .24 kg m^2.
Any thoughts?
George3 said:BUMP... FINAL TOMORROW NEED HELP ON THIS
I really need help on this. And to the previous poster the moment of inertia of a hollow sphere is bigger than that of a solid so your method would not work...right?
AEM said:Well, I just computed your moment of inertia by doing what I told you to do and got the right answer. Your mistake is confusing a sphere with a spherical portion of the interior removed with a spherical shell.
By the way, you will have to compute the density of the material out of which the object is made.
George3 said:So did you take (2/5)MR^2 for both radii and then subtract the two moments of inertia? Which formula for I did you use??