Nthe equation z = ct + d, z is measured in meters and t is measured in seconds. what are the dimensions (units) of d?

In the equation we are given that z is the sum of the product of c and t and d. If z has a dimension or unit of measurement that is meters then, the product of c and t (ct) should also be in meters. Furthermore, the unit of measurement of d should also be in meters. Thus, the answer is meters. 

  concave means having an outline or surface that curves inward like the interior of a circle or sphere. so the mirror curves inward.

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.