SOLUTION: In the equation s=ut=1/2at^2 why is A (9.81) negative

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Question 890382: In the equation s=ut=1/2at^2 why is A (9.81) negative
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
By convention, the y axis represents height.

y = 0 represents the ground and y = 10 represents 10 ft off the ground (or 10 m, 10 cm, whatever unit you're using)

Since gravity pulls the object down, and because the negative direction on the y axis is pointed down, it makes sense to say a+=+-9.81. This ensures we have an upside down parabola.