How to get the radius from the circumference?

Why is the energy that results from a roller coaster's position at the top of a hill referred to as potential energy?

Explain why electric current cannot exist if a current doesn't have a voltage source.

14. a body is projected with velocity vi from a.at the same time another body is projectedvertically upwards from point b withvelocity v2 lies vertically below the highestpoint. both the bodies collide thenv2÷v1is