I am using an equation for constant acceleration to find velocity. v^2=v(initial)^2+2a(x-x(initial)) Dropping a rock from 4 meters to the ground. Initial velocity is 0, a=9.8, and displacement is -4. So v^2=2(9.8)(-4), and it SHOULD equal=-8.85m/s (I know this is the correct answer, I already got it right on my homework). The velocity should be negative. But obviously my above answer is impossible because you can't take the square root of a negative. When using these constant acceleration equations I make the addition sign in the above equation negative if it is going upward (makes sense since gravity is working against it), and positive if it is going downward . Do I apply the negative sign after I solve, to show the direction? That just doesn't seem right. Help!