Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 4 - Section 4.5 - Exponential and Logarithmic Functions - 4.5 Exercises - Page 369: 96

Answer

after about $10.4$ seconds.

Work Step by Step

Solve for $t$ when $v(t)=-70$ ( downwards, velocity is negative). $80(e^{-0.2t}-1)=-70 \qquad$ ... $/\div 80$ $e^{-0.2t}-1=-\displaystyle \frac{7}{8} \qquad$ ... $/+1$ $e^{-0.2t}=\displaystyle \frac{1}{8} \qquad$ ... apply $\ln$() to both sides $-0.2t=\displaystyle \ln(\frac{1}{8}) \qquad$ ... $/\div(-0.2)$ $t=\displaystyle \frac{\ln(\frac{1}{8})}{-0.2}\approx 10.4$ seconds.
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.