Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 1 - Equations and Inequalities - Test - Page 182: 23

Answer

(a) $1\ sec$ and $5\ sec$ (b) $6\ sec$.

Work Step by Step

(a) Given the model equation $s = -16t^2 + 96t$, let $s=80$, we have $-16t^2 + 96t=80\longrightarrow t^2-6t+5=0\longrightarrow (t-1)(t-5)=0$, thus $t=1\ sec$ and $t=5\ sec$ (b) When it returns to the ground, $s=0$, we have $-16t^2 + 96t=0$ which gives $t=0$ and $t=6\ sec$. Discard $t=0$ as it is the starting point, thus we have $t=6\ sec$.
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