SOLUTION: A ball thrown with velocity of 28 meters per second from a cliff that is 40 meters high. h=-4.9t^2-28t+40. Find the time it takes the ball to hit the ground. Round to nearest tenth

Algebra ->  Expressions -> SOLUTION: A ball thrown with velocity of 28 meters per second from a cliff that is 40 meters high. h=-4.9t^2-28t+40. Find the time it takes the ball to hit the ground. Round to nearest tenth      Log On


   

Question 1089502: A ball thrown with velocity of 28 meters per second from a cliff that is 40 meters high. h=-4.9t^2-28t+40. Find the time it takes the ball to hit the ground. Round to nearest tenth of a second?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
When the ball hits the ground, +h=0+, so
+-4.9t%5E2+-+28t+%2B+40+=+0+
+-49t%5E2+-+280t+%2B+400+=+0+
+-7t%5E2+-+40t+%2B+400%2F7+=+0+
Use quadratic formula
+t+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
+a+=+-7+
+b+=+-40+
+c+=+400%2F7+

+t+=+%28+40+%2B-+sqrt%28+1600+%2B+1600+%29%29%2F%28-14%29+
+t+=+%28+40+%2B-+sqrt%28+3200+%29%29%2F%28-14%29+
+t+=+%28+40+-+56.57+%29+%2F+%28-14%29+
+t+=+16.57%2F14+
+t+=+1.18+
The ball hits the ground in 1.2 sec
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