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.

Algebra ->  Quadratic Equations and Parabolas -> 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.       Log On


   

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) About Me  (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.
graph%28300%2C300%2C-10%2C10%2C-10%2C120%2C-16x%5E2%2B84x%29

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
When it hits the ground, +h%28t%29+=+0+
+0+=+-16t%5E2+%2B+84t+
+t%2A%28+-16t+%2B+84+%29+=+0+
+16t+=+84+
+t+=+5.25+ sec
--------------------------
check:
+-16%2A5.25%5E2+%2B+84%2A5.25+=+0+
+-16%2A27.5625+%2B+441+=+0+
+-441+%2B+441+=+0+
OK