# Homework Help: Simple Moment of Inertia Question

1. Jan 2, 2009

### tachu101

1. The problem statement, all variables and given/known data
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...

2. Relevant equations

I=mr^2

3. 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?

2. Jan 3, 2009

### djeitnstine

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

3. Jan 3, 2009

### Staff: Mentor

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?