SOLUTION: You drop a ball from a set of bleachers that is 64 feet above the ground. How long will it take the ball to hit the ground? {{{h=-16t^2+s}}} So far, I have done this... {{

Algebra ->  Radicals -> SOLUTION: You drop a ball from a set of bleachers that is 64 feet above the ground. How long will it take the ball to hit the ground? {{{h=-16t^2+s}}} So far, I have done this... {{      Log On


   

Question 442973: You drop a ball from a set of bleachers that is 64 feet above the ground. How long will it take the ball to hit the ground?
h=-16t%5E2%2Bs
So far, I have done this...
h=-16t%5E2%2Bs
h=-16t%5E2%2B64
But I don't know what to do next to complete the problem. Thanks in advance!
Answer by swincher4391(1107) About Me  (Show Source):
You can put this solution on YOUR website!
Great job so far.
It will make sense when you think of it in these terms.
What height is the ground? Well, when we say we're 64 feet above the ground, and we let our s be 64, then we are saying we are 64 above 0. This implies that the ground is height 0. You may say, duh, but now we have the key to the problem.
Solve for t when h =0.
Then, +0+=+64+-+16t%5E2
Notice that 64 and 16t^2 are perfect squares.
Recall the difference of perfect squares %28a%5E2-b%5E2%29+=+%28a-b%29%28a%2Bb%29
Then, 64-16t%5E2+=+%288-4t%29%288%2B4t%29
Solve 8-4t = 0:
8+=4t
t+=+2
Solve 8 +4t = 0
8+=+-4t
t+=+-2
In this context, a negative time does not make sense, but a positive time does.
So the only time that makes LOGICAL SENSE is t = 2.
So t=2.
Hope this helped!