Physics for Scientists and Engineers 3rd Edition by Randall Knight, Chapter 1 Conceptual Question 4

Does the object represented in Figure Q1.4 have a positive or negative value of $\displaystyle a_x$ ? Explain.

Figure Q1.4

Solution:

Because the velocity vectors get longer for each time step, the object must be speeding up as it travels to the left. The acceleration vector must therefore point in the same direction as the velocity, so the acceleration vector also points to the left. Thus, $\displaystyle a_x$ is negative as per the convention in the book.

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