free fall equation

hi , with the free fall equation, in my book it is refererd to as either 4.9^2 or -4.9^2 , so which one is right, very confused

Dave

you choose the "positive" direction at the start of every calculation, so either can be correct.

if you choose "up" as the positive direction, then accelleration due to gravity is

if you choose "down" as the positive direction, then accelleration due to gravity is

what is ment by up or down as the positive direction?

thanks for your reply

the direction which you have to be travelling in to have a positive velocity.

so if "down" is the positive direction, and an object is falling from the top of a building, it will have a positive velocity.

thanks , that simple .thank you for your time

Dave