# Simple Moment of Inertia Question

by tachu101
Tags: inertia, moment, simple
 P: 74 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?
 PF Gold P: 619 You are correct. The definition of moment of Inertia is $$\sum_{i} m_{i} r^{2}_{i}$$
Mentor
P: 40,871
 Quote by tachu101 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?

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