1. The problem statement, all variables and given/known data A long, straight, and massless rod pivots about one end in a vertical plane. In configuration I, two small identical masses are attached to the free end; in configuration II, one mass is moved to the center of the rod. What is the ratio of the frequency of small oscillations of configuration II to that of configuration I? (A) (6/5)^1/2 (the correct answer) (B) (3/2)^1/2 (C) 6/5 (D) 3/2 (E) 5/3 2. Relevant equations Angular Frequency of a physical pendulum of length L with a mass at its endpoint: sqrt(g/L) "The center of mass of a system moves as if it were a single particle of mass equal to the total mass of the system, acted on by the total external force, and independent of the nature of the internal forces" (Marion and Thornton page 333) 3. The attempt at a solution Why is it wrong to apply the quote from Marion and Thornton and say that this situation is equivalent to the situation of having a physical pendulum of length 3/4 L with both of the masses at the endpoint?