Fundamentals of Physics Extended (10th Edition)

Published by Wiley
ISBN 10: 1-11823-072-8
ISBN 13: 978-1-11823-072-5

Chapter 2 - Motion Along a Straight Line - Problems - Page 33: 20d

Answer

a(t) is positive if when $t\lt0$

Work Step by Step

The equation for acceleration in this situation is a(t)=-30t. This means that whenever t is less than 0, acceleration will be negative, for the coefficient in front of t is negative, and a negative times a negative is a positive.
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