Simple Moment of Inertia Question

[tachu101]

Homework Statement

A rod of negligible mass is pivoted about one end. Masses can be attached to the rod at various positions along the rod. Currently, there is a mass (m) attached a distance (L) from the pivot. To increase the moment of inertia about the pivot by a factor of 5, you must attach...

Homework Equations

I=mr^2

The Attempt at a Solution

Io= mL^2
If= 5(Io) = mL^2(original mass)+4(mL^20) All I did was add four more masses of equal size at a distance L from the pivot. Is there another solution?

 

[djeitnstine]

You are correct. The definition of moment of Inertia is \sum_{i} m_{i} r^{2}_{i}

 

[Doc Al]

All I did was add four more masses of equal size at a distance L from the pivot. Is there another solution?

Sure, there are plenty of solutions. The question is a bit vague. Are there any constraints given? (Such as the the number of masses you are allowed to add or the size of the masses.)

For example: What if you could only add a single mass of equal size. How could you solve the problem then?