If a ball is thrown directly upward with a velocity of 20 ft/s, its height (in feet) after t seconds is given by y = 20t − 16t2. What is the maximum height attained by the ball? (Round your answer to the nearest whole number.)

Question

anonymous · Answer

y = 20t − 16t^2

anonymous · Answer

max is at the second coordinate of the vertex
the first coordinate of the vertex is $t=-\frac{b}{2a}$ which in your case is $-\frac{20}{2\times (-16)}=\frac{5}{8}$

anonymous · Answer

replace $t$ by $\frac{5}{8}$ to get the maximum height 
use a calculator

anonymous · Answer

i get this http://www.wolframalpha.com/input/?i=20*%285%2F8%29-16%285%2F8%29^2

anonymous · Answer

I just got that. thanks :)