# Rotating half cylinder energy and power calculation

1. Dec 16, 2011

### crf59

Hi folks,

I'm an ocean engineer who's getting old and slow. If I have a half-cylinder mass on a shaft where I'd like to be able to quantify energy (which I think I have right) and then have some way of relating that to potential power output.

What I have so far:
m=18.6 kg
Length=0.305m
radius=0.07m
Mass moment of inertia (I) = 0.5mr^2
Rotational KE (Er) = 0.5Iw^2
w=60rpm=0.159 rad/s

I calculate the Er as 0.00747J

Does this jive? Is there any meaningful way of relating that to power? I do not have a load value (yet), so am just trying to understand what this might be in terms of power if I use some conversion efficiency (thinking alternator load). I am assuming the same motive force that accelerated it to 60 rpm is constant (in some sort of resonance). If I have my calcs/assumptions wrong so far, please correct.

2. Dec 17, 2011

### Redbelly98

Staff Emeritus
Welcome to Physics Forums.

You're general approach is correct. However, 60 rpm is actual 2*pi rad/s. I get 0.90 J for the energy. (I=0.046 kg-m2)

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