# Homework Help: Power produced by a rotation disk

1. Sep 27, 2010

### kenshin6249

how do i calculate the power produced by a rotating disc?

for example given that the constant angular velocity is 30rad/s, diameter of disc is 0.5m, mass is 15kg.

or do u need more data to calculate the power? if yes, what data do u need?

2. Sep 27, 2010

### rock.freak667

The power generated is Fv, in rotational terms, it turns out as Tω where 'T' is the torque producing the rotation.

You can further get the 'T' by using T=Iα where 'I' is the moment of inertia of the disc about the center of rotation and 'α' is the angular acceleration.

What other parameters do you have to work with?

3. Sep 27, 2010

### kenshin6249

how do i calculate angular acceleration from the given data?
with constant angular velocity do it have angular acceleration?

4. Sep 27, 2010

### rock.freak667

Do you have the time it took for the disc to reach 30 rad/s?

5. Sep 27, 2010

### kenshin6249

nop it is just spinning at that speed from the start to the end.

6. Sep 27, 2010

### rock.freak667

I am not sure you can get the power just with the angular velocity and the moment of inertia. You can find the rotational energy produced using E=0.5Iω2 though.

7. Sep 27, 2010

### kenshin6249

yes that one i know.

is something similar to finding the power output of a turbine connected to a shaft onto a flywheel. the flywheel is spining in constant angular velocity by connecting it to a generator or a dynamo to producing a power output.

i need to find the power generated before entering the dynamo or without a dynamo.

8. Sep 27, 2010

### rock.freak667

Well the most you can get given your information is the kinetic energy (J) and not the power (W).

9. Sep 27, 2010

### kenshin6249

with the fluid pushing the shaft to turn there is an energy = 0.5mv2 = E1.
the power of the fluid = $$\rho$$*g*h*Q = P1

with the rotating shaft energy = 0.5Iω2 = E2

with 2 differnt energy we can determine the efficiency.

efficiency = $$\frac{E2}{E1}$$ = $$\frac{P2}{P1}$$

from here we determine the P2.
is it correct?

Last edited: Sep 27, 2010
10. Sep 27, 2010

### rock.freak667

Yes that should work as well.