are

(1) v=u+at

(2) S = ut + ½at²

and (3) v²=u²+2aS

Where S=displacement, u=initial velocity, v=final velocity, t=time, a=acceleration.

When a projectile is fired upward, the gravitational force of earth tends to retard the motion of the projectile. The acceleration due to gravity,

g=9.8 m/s².

Since this acts against the upward motion, a has to be taken as negative.

Moreover, all the quantities should be converted to SI Units.

With these hints, please try to solve the problem.]]>

I've gotten

16t^2= 125 + s and get 31.25 seconds?? am I close???