A horizontal tree branch is directly above another horizontal tree branch. The elevation of the higher branch is 9.45 m above the ground, and the elevation of the lower branch is 5.58 m above the ground. Some children decide to use the two branches to hold a tire swing. One end of the tire swing's rope is tied to the higher tree branch so that the bottom of the tire swing is 0.46 m above the ground. This swing is thus a restricted pendulum. Starting with the complete length of the rope at an initial angle of 14.6° with respect to the vertical, how long does it take a child of mass 28.5 kg to complete one swing back and forth?
The Attempt at a Solution
I used the T=2∏√I/mgd equation, but I'm having trouble finding d because I don't know where the center of mass is. Also, What branch would I use?