A projectile is launched horizontally from a that is 10.0m above the ground with an initial velocity of 5.00 m/s. How far from the base of the chief does land?

Light from the sun reaches the earth in 8.3 minutes. the velocity is 3.00 x 10^8 m/s. how far is earth from the sun? i know how to get to d = (3 x 10^8 m/s)(498 sec). i just don't know how to get from there to the answer being 1.5 x 10^11 m.

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 •  

The voltage applied across a given parallel-plate capacitor is doubled. how is the energy stored in the capacitor affected?