One afternoon I was sitting on a bench in the park when a boy went running by me and then lept into a swingset that was just hanging there at rest. I noticed when this happened the swingset swung about 65.0° up from the vertical. The length of the chain of the swing set couldn't be more than 2.00 m. Typically people can run about 5.00 m/s. Assuming the chain has no mass, and the swingset seat was about 2.00 kg, what was the boy's mass.