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.
chess10771
Messages
9
Reaction score
0

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
 
Physics news on Phys.org
(a) What is the formula for the volume of a sphere?
 

Thread 'Rolling without slipping on a curved surface'

Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
View full post »

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »

Similar threads

HELP - ROTATIONAL INERTIA (no numbers given)
Replies
3
Views
4K
Rotational Inertia: Hoop vs Disk
Replies
19
Views
4K
What is the "r" in the moment of inertia?
Replies
13
Views
2K
Correct Use of the Parallel Axis Theorem for Moment of Inertia
Replies
2
Views
2K
Does the mass of an object affect its inertia?
Replies
6
Views
2K
Angular Momentum Problem: Mouse walking on a rotating turntable
Replies
5
Views
1K
Moment of inertia of a disk about an axis not passing through its CoM
Replies
11
Views
3K
Angular momentum and rotational inertia
Replies
25
Views
3K
Deriving the moment of inertia of a sphere
Replies
6
Views
2K
Rotational Inertia and Net Torque with Friction
Replies
10
Views
3K

Hot Threads

Recent Insights

Back
Top