A football on the moon (1/6 earth's gravity) is kicked straight up with an initial velocity of +14.5 m/s. If it starts 2.7 m above the surface, how much time has passed until it is 16.8 m above the surface and on its way down?

Answer 1

16.8 = 2.7 + 14.5 t -(1/12)9.8 t^2
or
14.1 = 14.5 t - .817 t^2

t^2 -14.5 t + 14.1 = 0

t = [ 14.5 +/- sqrt (14.5^2 -4*14.1) ]/2

t = [ 14.5 +/- 12.4 ] / 2

= 1.05 or 13.5
the 1.05 is on the way up
so the answer is 13.5 seconds