SOLUTION: Jack hit a golf ball from the ground and its movement follows the equation h(t)=-16t^2+84t, where t is the time in seconds, and h(t) is the height of the ball at a given time t.

Question 1138655: Jack hit a golf ball from the ground and its movement follows the equation h(t)=-16t^2+84t, where t is the time in seconds, and h(t) is the height of the ball at a given time t.
Find the time that it took the golf ball to hit the ground again correct to two decimal places.
seconds

Found 2 solutions by Boreal, josmiceli:
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
set the equation -16t^2+84t=0, since the ground is presumably at h(t)=0
-4t(4t-21)=0
t=0 (at the start)
t=21/4=5.25 seconds.

Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
When it hits the ground,

sec
--------------------------
check:

OK
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