Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 4 - Section 4.9 - Antiderivatives - 4.9 Exercises - Page 357: 68

Answer

After $5$ seconds, the first ball passes the second ball when both balls are at a height of 272 feet.

Work Step by Step

We can write an equation for the vertical position of the first ball: $s_1(t) = -16t^2+48t+432$ We can write an equation for the vertical position of the second ball: $s_2(t) = -16(t-1)^2+24(t-1)+432,~~~~~t \geq 1$ Note that the second ball is thrown 1 second later, so we need to adjust the second equation by 1 second. We can find $t$ when $s_1 = s_2$: $s_1 = s_2$ $-16t^2+48t+432 = -16(t-1)^2+24(t-1)+432$ $-16t^2+48t = -16(t^2-2t+1)+24t-24$ $-16t^2+48t = -16t^2+32t-16+24t-24$ $48t = 32t-16+24t-24$ $8t = 40$ $t = 5$ After $5$ seconds, the first ball passes the second ball. We can verify this by finding the height of each ball after 5 seconds: $s_1(5) = -16(5)^2+48(5)+432 = 272$ $s_2(5) = -16(5-1)^2+24(5-1)+432 = 272$ After $5$ seconds, the first ball passes the second ball when both balls are at a height of 272 feet.
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