A bullet is fired upward from ground level. It’s height above the ground (in feet) at time t seconds is given by h= -16t^2 +1000t. How many seconds does it take the bullet to return to ground level?

Answer 1

0 = -16t^2 + 1000t

0 = 4t^2 - 250t <--- divides by -4

0 = 2t^2 - 125t <--- divides by 2

0 = t(2t - 125) <--- factors out t

t = 0 or 2t - 125 = 0

t=0 or t = 125/2 = 62.5

62.5 seconds