when is the value of g negetive and positive is it while its moving down or up ??

It doesn`t really matter if you use +9.8 m/s/s or -9.8 m/s/s, as long as you`re consistent with what you choose. What I mean is that there`s no intrinsic reason to say that down is negative and up is positive, or the other way around. Although the general convention is to use down as negative, there`s nothing wrong with doing the same problem with down as positive. The only difference is your answers with each method will be opposites of one another

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