A ball is projected upward at time t = 0.0 s, from a point on a roof 40 m above the ground. The ball rises, then falls and strikes the ground. The initial velocity of the ball is 15.4m/s. Consider all quantities as positive in the upward direction. The time when the ball strikes the ground is closest to:

Answer 1

hf=hi+vi*t-1/2 g t^2
0=40+15.4*t-4.9t^2
this is a quadratic, use the quadratic equation to find time t

Answer 2

-1.69