In projectile motion, the final velocity (Vf) at y = 0 is equal in magnitude to the initial velocity (V0) but opposite in direction, assuming no air resistance. This means that while the speeds are equal, the velocities differ due to their directions. If external forces like air resistance are considered, Vf will be less than V0. The conservation of energy principle supports this, as the kinetic and potential energy balance leads to the conclusion that |V0| = |Vf| when the object reaches the ground. Thus, the final velocity is not zero but rather equal in magnitude to the initial velocity just before impact.