Question

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

Answer 1

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