Giancoli's Physics: Principles with Applications, 7th Edition

2

Describing Motion: Kinematics in One Dimension

Change chapter2-1 to 2-3: Speed and Velocity

2-4: Acceleration

2-5 and 2-6: Motion at Constant Acceleration

2-7: Freely Falling Objects

2-8: Graphical Analysis

Question by Giancoli, Douglas C., Physics: Principles with Applications, 7th Ed., ©2014, Reprinted by permission of Pearson Education Inc., New York.

Problem 19

Q

A

- $6.0\textrm{ m/s}^2$
- $0.61\textrm{ g's}$

In order to watch this solution you need to have a subscription.

VIDEO TRANSCRIPT

This is Giancoli Answers with Mr. Dychko. The acceleration of this sports car is gonna be the change in velocity divided by time. So the final velocity is zero and the initial velocity is 120 meters divided by 5 seconds that's 24 meters per second. So we take the difference there, zero minus 24 meters per second divided by the time it spends braking— 4 seconds— and we get negative 6.0 meters per second squared and the magnitude of that acceleration is 6.0 meters per second squared. And then expressing that in units of *g*'s there's 1 *g* for every 9.8 meters per second squared and so these meters per second squared's, you can think of it as a single package unit cancel and we are left with 0.61 *g*'s is the acceleration.

COMMENTS

By swedesanddanes on Mon, 10/12/2015 - 8:58 PM

Why did the magnitude become positive? Wouldn't it have remained negative because the car is braking to a complete stop, thus decreasing its acceleration?

Thanks!

By Mr. Dychko on Tue, 10/13/2015 - 3:01 AM

Hi swedesanddanes, the answer to your question is in the word **magnitude**. That word means **size**. It means ignore direction, and so ignore the negative sign. **magnitudes** are always positive.

All the best,

Mr. Dychko

Giancoli Answers, including solutions and videos, is copyright © 2009-2024 Shaun Dychko, Vancouver, BC, Canada. Giancoli Answers is not affiliated with the textbook publisher. Book covers, titles, and author names appear for reference purposes only and are the property of their respective owners. Giancoli Answers is your best source for the 7th and 6th edition Giancoli physics solutions.