SOLUTION: h=-16t^2+48t+160 how many seconds til it hits the ground?

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Question 44144: h=-16t^2+48t+160
how many seconds til it hits the ground?
Answer by adamchapman(301) About Me  (Show Source):
You can put this solution on YOUR website!
h= height
h=-16t%5E2%2B48t%2B160
when it hits the ground, h=0. So:
-16t%5E2%2B48t%2B160=0
Use the quadratic solver t+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
where
a=-16
b=48
c=160
Now: t+=+%28-48+%2B-+sqrt%28+48%5E2-4%2A%28-16%29%2A160+%29%29%2F%282%2A%28-16%29%29+
t+=+%28-48+%2B-+sqrt%28+2304%2B10240%29%29%2F-32+
t+=+%28-48+%2B-+sqrt%28+12544%29%29%2F-32+
t+=+1.5+%2B-+112%2F-32+
t+=+1.5+%2B-+3.5+
So t=-2 or t=5
t=-2 would mean going back in time, which i think is impossible, so th must be 5 seconds.
I have graphed heigt with time below. This should confirm that h=0 when t=5.
+graph%28+300%2C+200%2C+0%2C+6%2C+-1%2C+200%2C+-16x%5E2%2B48x%2B160%29+
I hope this helps
P.S. I am trying to start up my own homework help website. I would be extremely grateful if you would e-mail me some feedback on the help you received to adam.chapman@student.manchester.ac.uk