Problema Solution
A ball is thrown vertically upward from the ground. Its distance in feet from the ground in t seconds is s= -16t^2 +96t. After how many seconds will the ball be 128 feet from the ground?
Answer provided by our tutors
s= -16t^2 +96t
we need to find t such that s = 128 that is
-16t^2 +96t = 128
-16t^2 +96t - 128 = 0 divide both sides by -16
t^2 - 6t + 8 = 0
by solving the quadratic equation we find
t = 2 seconds that is, after 2 seconds the ball will be 28 feet from the ground
t = 4 seconds that is, after 4 seconds the ball will be 28 feet from the ground