# Moment of inertia of this body

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1. Jan 10, 2017

### Mohamed Essam

1. The problem statement, all variables and given/known
See attachment , it only gives me length of rod and it's mass and radius of sphere and its mass and the place of the axis

2. Relevant equations
I=mr^2

3. The attempt at a solution
I tried to get the moment of intertia of rod by integration from -L/4 to 3L/4 , but i cannot get the intertia of sphere around the axis ,

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• ###### IMG_0497.JPG
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Last edited by a moderator: Jan 10, 2017
2. Jan 10, 2017

### Staff: Mentor

Can you post a better image please? That one is way too dark to read...

3. Jan 10, 2017

### Mohamed Essam

4. Jan 10, 2017

### haruspex

You should not need to do any integration. For such a question, I would expect to be allowed to quote standard formulas for moments about mass centres and apply the parallel axis theorem.

5. Jan 10, 2017

### Mohamed Essam

by this equation ( Inertia at axis =Inertia at axis from centre of mass + mass*distance between the two axis^2 ) ??

6. Jan 10, 2017

### haruspex

Yes.

7. Jan 10, 2017

### Mohamed Essam

Thank you for telling me the way of parallel axis theorem i wasn't know it , my physics professor in university didn't tell us anything about it and he puts it in an exam

8. Jan 10, 2017

### haruspex

That's quite an omission. All good now?

9. Jan 10, 2017

### Mohamed Essam

Yeah , thank you so much.