What is the algebraic expression for the speed vb of the lighter box as it reaches b? express your answer in terms the box's speed va at point a, the magnitude g of the acceleration due to gravity, and the heights, ha and hb, of the two points above the ground.

stands for electromotive force and it is measured in volts. despite its name, it is not actually the force in the sense of being a "pushing" or "pulling" (not measured in newtons).an equation that relates emf,  ℰ,  to a battery's terminal voltage, v, current, i, and internal resistance, r, is    ℰ = v + irin this case, the emf can be interpreted as a voltage—a difference in electric potential.i would not say that it would be considered an energy. if emf can be defined as the energy/work per a unit charge from a battery or other electric source, then it is not strictly energy.

Newton's first law describes something special that results from the sum of all the external forces (including gravity) on an object. 

Electric force between two charged object varies inversely as the square of distance between them (coulomb's law). this means if two charged objects move away force between them decreases.