Question

When we use  'g' as positive and negative in motion under gravity.? Please explain I'm always confused in this.

Solution

The signs of g and u depends on the conventions you are applying. if you take upward direction as positive, then g is negative as it acts downwards. if you take downward direction as positive, then g is positive. generally, upward is taken positive and g negative. also u depends on inital conditions. if you throw a ball upward, u is positive, while g is negative            (acc. to first convention) if a ball is dropped from a height, u is negative, g is also negative   (acc. to first convention)

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