But before we do that you might say "well whats the acceleration vector going to be if we think about it in two dimensions" well the acceleration vector is the acceleration due to gravity on an object in free fall near the surface of the planet, so this is going to be, its not going to have any x component - I can just write zero I don't have to write that - and its y component is negative 9.8, I won't write the units here for this problem to save space negative 9.8 meters per second squared in the vertical direction, so if we scale the 'j' vector by negative 9.8 the negative points it down and then we scale it by 9.8 this is the acceleration due to gravity.