SOLUTION: How long would it take a ball dropped from the top of a 81 foot building to hit the ground? I have no idea how to solve this.

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: How long would it take a ball dropped from the top of a 81 foot building to hit the ground? I have no idea how to solve this.      Log On


   

Question 645947: How long would it take a ball dropped from the top of a 81 foot building to hit the ground?

I have no idea how to solve this.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
You need to find +h%28t%29+ where +h+ is
the height above ground, and t is the time in seconds
for the ball to hit the ground. The equation is:
+h%28t%29+=+-16t%5E2+%2B+81+
In words:
( height above ground ) = ( effect of gravity pulling down ) + ( starting height above ground )
Note that at +t=0+ when the ball hasn't started dropping yet
+h%280%29+=+-16%2A%280%5E2%29+%2B+81+
+h%280%29+=+81+ ft ,as it should be
----------------------------
When the ball hits the ground, the height is zero, so
+0+=+-16t%5E2+%2B+81+
+16t%5E2+=+81+
+t%5E2+=+%28+9%2F4+%29%5E2+
+t+=+9%2F4+ and
+t+=+2.25+ sec
It takes the ball 2.25 sec to hit the ground