# Wrong answer in textbook

## Homework Statement

(Problem about a collision) (...). What then is their velocity in (a) unit-vector notation and as (b) magnitude and (c) angle.

I will not post the problem due to copyright issues and that it is absolutely pointless now.

## The Attempt at a Solution

I was able to solve (a) and (b).
However, my answer for (c) differs from that of the textbook.
$$\text{a)} \;(2.67 \;\text{m/s})\hat{i}+(-3.00 \;\text{m/s})\hat{j}$$
$$\text{b)} \;4.01 \;\text{m/s}$$
$$\text{c)} \;\theta{} = \tan^{-1}\left(-\frac{3.00}{2.67}\right)=-0.845397=-48.4^{\circ{}}$$

While the book provides +48.4° as the angle.

Am I correct? You can solve (c) from (a) and (b) [my answers are identical to those of the book].

It is from Fundamentals of Physics (Extended) - 9th ed.

## Answers and Replies

Well, without thinking too much about it, the vector given in (a) is in the fourth quadrant. The angle 48.4° is in the first quadrant. Your answer, however, is definitely in the fourth quadrant.

TSny
Homework Helper
Gold Member
You are correct. The text should not have stated the answer as simply 48.4o.
If they had stated it as 48.4o below the positive x direction, then that would have been a good answer. But they didn't.

Yes, that's what I thought. I was pretty sure I was right, but as this book has presented very few mistakes already I thought I could be missing something.

Thank you guys for looking at it.