A ball is thrown straight upward from ground level with a velocity of 18m/s How much time passes before the ball strikes the ground? Disregard air resistance.

The displacement of the ball can be calculated using:

s = ut + 1/2 at²; where u is the initial velocity and a is the acceleration. Because these are in opposite directions, one will be given a negative sign.

s = 0 at ground level

s = 18t - 1/2 x 9.81t²

t (18 - 4.9t) = 0

t = 0; t = 3.67 seconds

Thus, the ball will come back and strike the ground at 3.67 seconds.