A rock with a mass of 5-kg and moving at 20 m/s collides head on with a 10-kg rock. After the collision, both rocks come to rest. Determine the initial velocity of the 10-kg rock.

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Sorry i don’t know what to do

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.

I’m not sure about this question