Question

what is the initial velocity (Vyo) of a projectile launched horizontally? why?

i know that it is 0 m/s, but i don't know why/how to explain it.

Answer 1

The intial velocity? it is the launching velociy, in the horizontal, it vo*cosTheta. For theta=zero, the horizontal velocity is vo. For the vertical, it is vo*sinTheta, and for vertical velocity voy, sinTheta is zero (for theta=zero).