Giancoli 7th Edition textbook cover
Giancoli's Physics: Principles with Applications, 7th Edition
Describing Motion: Kinematics in One Dimension
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2-1 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 4

A rolling ball moves from x1=8.4 cmx_1 = 8.4 \textrm{ cm} to x2=4.2 cmx_2 = -4.2 \textrm{ cm} during the time from t1=3.0 st_1 = 3.0 \textrm{ s} to t2=6.1 st_2 = 6.1 \textrm{ s}. What is its average velocity over this time interval?

4.1 cm/s-4.1\textrm{ cm/s} Note: the video has incorrect units of  m/s\textrm{ m/s}, but it should be  cm/s\textrm{ cm/s}.
Giancoli 7th Edition, Chapter 2, Problem 4 solution video poster

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This is Giancoli Answers with Mr. Dychko. To calculate the average velocity, we take the difference in position divided by the change in time. So at time t 2, it's at position negative 4.2 centimeters and at time t 1, it's at position 8.4 centimeters and so we take the difference between their positions— negative 4.2 centimeters minus 8.4— and divide by the change in time— t 2 is 6.1 seconds and t 1 is 3.0 seconds. Divide this top difference by the bottom difference and you end up with negative 4.1 meters per second is the average velocity.

By joseotilio25 on Sun, 2/22/2015 - 5:25 PM

Why m/s if I have cm/s

By Mr. Dychko on Sun, 2/22/2015 - 10:12 PM

Hi joseotilio25, because... I made a typo! Thanks a lot for catching that. I've made a note above the video, and updated the quick answer. The units should be cm/s\textrm{cm/s}, as you say.

Mr. Dychko

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