Moment of inertia formulas for pulley and composite system

[ktvphysics]

Answer check please -- Moment of Inertia Calculations

For question 1 I got T=m_nut * r _pulley * gravity

For question 2 I got I_system = 1/2 M(R²₃ + R²₄ + m (R²₁ + R²₂)

First day of physics lab and I just wanted to double check that these are correct.

Thanks.

 

[tiny-tim]

hi ktvphysics! welcome to pf!

(1 is fine)

i think you're misunderstanding the diagram for 2 …

the CD and the washers both have holes in the middle

also (although the question doesn't say), it must be asking for the moment of inertia about the centre, so you'll have to use the parallel axis theorem for the two washers!

 

[ktvphysics]

hi ktvphysics! welcome to pf!

(1 is fine)

i think you're misunderstanding the diagram for 2 …

the CD and the washers both have holes in the middle

also (although the question doesn't say), it must be asking for the moment of inertia about the centre, so you'll have to use the parallel axis theorem for the two washers!

So the answer to 2 would be:

I_system = 1/2 M(R²₃ + R²₄) + 2[1/2m(R²₁ + R²₂) + md²]

That corrects the problem about the Parallel Axis Theorem, but I'm confused about what you were saying about the holes in the middle. I used the moments of inertia for hollow cylinders for the CD and Washers, which is essentially what each of them is.

 

[tiny-tim]

hi ktvphysics!

That corrects the problem about the Parallel Axis Theorem, but I'm confused about what you were saying about the holes in the middle. I used the moments of inertia for hollow cylinders for the CD and Washers, which is essentially what each of them is.

sorry, i was in a hurry to go out and i misremembered the formula!

yes, your answer is fine now ​