velocity at the highest point is 0
and velocity is not acceleration...
velocity is expressed in m/s (or something similar)
while acceleration is expressed in m/s/s or m/s² or an equivalent....
g = 9.81m/s² -> an acceleration, not a velocity (it's constant, so at the highest point the velocity is 0 and the acceleration is 9.81m/s² aimed downwards towards the earth)
try to read a little bit more about it and try to understand what you're calculating, physics really isn't that hard once you know what you're doing ... (especially in highschool you can ace it if you're dedicated)
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