SOLUTION: Lewis Tower in Philadelphia is 400 ft. high. Suppose that a ball is projected upward from the top of the tower, and its position in feet above the ground is given by the quadratic

Algebra ->  Pythagorean-theorem -> SOLUTION: Lewis Tower in Philadelphia is 400 ft. high. Suppose that a ball is projected upward from the top of the tower, and its position in feet above the ground is given by the quadratic       Log On


   

Question 369002: Lewis Tower in Philadelphia is 400 ft. high. Suppose that a ball is projected upward from the top of the tower, and its position in feet above the ground is given by the quadratic function defined by f(t)= -16t^2+45t+400, where t is the number of seconds elapsed. How long to the nearest 10th of a second will it take for the ball to reach a height of 200 ft. above the ground?
I used the pythagorean theorem but I got 6.6 and the answer is 5.2. I don't know what I am doing wrong.
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!


Hi,

position in feet above the ground  =  -16t^2+45t+400

How long will it take for the ball to reach a height of 200 ft. above the ground

200 = -16t^2+45t+400

16t^2 - 45t - 200 = 0

t+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+

t+=+%2845+%2B-+sqrt%28+14825%29%29%2F%2832%29+

t+=+%2845+%2B-+121.8%29%2F%2832%29+ Note: solution t < 0 cannot use

t = 166.8 /32 = 5.2 sec