Solve the problem
-A toy rocket is shot vertically upward from the ground. Its distance in feet from the ground in $t$ seconds is given by $\mathrm { s } ( \mathrm { t } ) = - 16 \left( \mathrm { t } ^ { 2 } \right) + 142 \mathrm { t }$. At what time(s) will the ball be $151 \mathrm { ft }$ from the ground? Round your answer to the nearest tenth of a second.
A) $1.2 \mathrm { sec }$ and $7.6 \mathrm { sec }$
B) $137.8 \mathrm { sec }$ and $146.2 \mathrm { sec }$
C) $8.9 \mathrm { sec }$
D) $4.4 \mathrm { sec }$

Question

Quizplus · Accepted Answer

To find when the ball will be 151 ft from the ground, set $s(t) = 151$ and solve for $t$: $151 = -16t^2 + 142t$. Rearranging gives $16t^2 - 142t + 151 = 0$. Solving this quadratic equation yields $t \approx 1.2$ and $t \approx 7.6$ seconds.

Solve the Problem -A Toy Rocket Is Shot Vertically Upward ttt

Solve the Problem
-A Toy Rocket Is Shot Vertically Upward $t$