At a time $t$ seconds after an object is tossed vertically upward, it reaches a height $s$ in feet given by the equation:
$$s = 128 t - 16 t ^ { 2 }$$
In how many seconds does the object reach its maximum height?
A) $\quad 8 \mathrm { sec }$
B) $\quad 128 \mathrm { sec }$
C) $\quad 4 \mathrm { sec }$
D) $256 \mathrm { sec }$
E) $\quad 2 \mathrm { sec }$

Question

Quizplus · Accepted Answer

To find the time at which the object reaches maximum height, we need to find the vertex of the parabola defined by the given equation. We can do this using the vertex formula:
$$t_{\text{max}} = - \frac {b} {2a} = - \frac {128} {2(-16)} = 4$$
Therefore, the object reaches its maximum height after 4 seconds (choice C).

At a Time ttt Seconds After an Object Is Tossed Vertically Upward, It Reaches

At a Time $t$ Seconds After an Object Is Tossed Vertically Upward, It Reaches