A student attaches a rope to a 9.5 kg box of books. He pulls with a force of 45 N at an angle of 30° with the horizontal. The coefficient of kinetic friction between the box and the sidewalk is 0.29. Find the acceleration of the box.

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.

If its history of, then b) because a) implies only present day (now)