Solve the problem.
-A ball is thrown vertically upward with an initial velocity of 128 feet per second. The distance in feet of the ball from the ground after $t$ seconds is $s = 128 t - 16 t ^ { 2 }$. For what intervals of time is the ball less than 240 above the ground (after it is tossed until it returns to the ground)?
A) between 0 and 3 seconds and between 5 and 8 seconds
B) between 3 and 5 seconds
C) between 0 and $2.5$ seconds and between $5.5$ and 8 seconds
D) between 0 and $3.5$ seconds and between $4.5$ and 8 seconds

Question

Quizplus · Accepted Answer

To find when the ball is less than 240 feet above the ground, set the equation $s = 128t - 16t^2 < 240$ and solve for $t$. Rearranging the inequality gives $16t^2 - 128t + 240 > 0$. Factoring or using the quadratic formula yields the roots $t = 3$ and $t = 5$. Therefore, the ball is less than 240 feet above the ground between 0 and 3 seconds and between 5 and 8 seconds.

Solve the Problem ttt Seconds Is s=128t−16t2s = 128 t - 16 t ^ { 2 }s=128t−16t2

Solve the Problem $t$ Seconds Is $s = 128 t - 16 t ^ { 2 }$