A45kg child swinging on a 7.0m long rope acts like a simple pendulum. what is the period of oscillation?

Consider a system to be two train cars traveling toward each other. what is the total momentum of the system before the train cars collide?   kg • what must the total momentum of the system be after the train cars collide?   kg •  

What component of earth’s atmosphere exists entirely as a result of photosynthesis?

The junction rule describes the conservation of which quantity? note that this rule applies only to circuits that are in a steady state.