A golfball is hit from ground level with an initial vertical velocity of 64 ft/s. After how many seconds will the ball hit the ground?

a. 3 seconds

b. 4 seconds

c. 5 seconds

d. 6 seconds

The ball hits the ground at unknown time (t) when the height (h) = 0

h (t) = - 16t² + vt + h ⇒ v = 64, h = 0, h (t) = 0, find t

0 = - 16t² + 64t

0 = - 16t (t - 4)

0 = - 16t or 0 = t - 4

t = 0 or t = 4

It starts at t = 0 seconds and ends at t = 4 seconds

Answer: B