SOLUTION: h = –16t2 + 40t + 8. The height h in feet of an object after t seconds is given by the function h = –16t2 + 40t + 8. How long will it take the object to hit the ground? R

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: h = –16t2 + 40t + 8. The height h in feet of an object after t seconds is given by the function h = –16t2 + 40t + 8. How long will it take the object to hit the ground? R      Log On

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Question 683924: h = –16t2 + 40t + 8.
The height h in feet of an object after t seconds is given by the function
h = –16t2 + 40t + 8.
How long will it take the object to hit the ground? Round your answer to the nearest thousandth.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
It reaches the ground when +h+=+0+
+h+=+-16t%5E2+%2B+40t+%2B+8+
+0+=+-16t%5E2+%2B+40t+%2B+8+
+0+=+-2t%5E2+%2B+5t+%2B+1+
Use the quadratic formula:
+t+=+%28-b+%2B-+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29%29+%2F+%282%2Aa%29+
+a+=+-2+
+b+=+5+
+c+=+1+
+t+=+%28-5+%2B-+sqrt%28+5%5E2+-+4%2A%28-2%29%2A1+%29%29+%2F+%282%2A%28-2%29%29+
+t+=+%28-5+%2B-+sqrt%28+25+%2B+8+%29%29+%2F+%28-4%29+
+t+=+%28-5+%2B-+sqrt%28+33+%29%29+%2F+%28-4%29+
+t+=+5%2F4+%2B+sqrt%2833%29%2F4+
+t+=+1.25+%2B+5.7446%2F4+
+t+=+1.25+%2B+1.4362+
+t+=+2.686+ sec
Here's a plot of the function:
+graph%28+400%2C+400%2C+-2%2C+4%2C+-1%2C+5%2C++-2x%5E2+%2B+5x+%2B+1+%29+