Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 6 - Dynamics I: Motion Along a Line - Exercises and Problems - Page 161: 7

Answer

a) $1.49\;\rm m/s^2,\;0\;m/s^2$ b) $-0.275\;\rm m/s^2,\;0\;m/s^2$

Work Step by Step

a) First of all, we need to analyze the 3-N force into its $x$ and $y$ components. From the geometry of the given figure, their components are $$F_{x }=3\sin20^\circ{\;\rm N},\;\;\;\;\;\;\;\;\;F_{y}=3\cos20^\circ{\;\rm N}$$ We know, from Newton's second law, that $$\sum F_{x }=ma_x,\;\;\;\;\;\;\;\;\;\sum F_{y}=ma_y$$ Thus, $$a_x=\dfrac{\sum F_{x }}{m}=\dfrac{5-1-3\sin20^\circ}{2}=\color{red}{\bf1.49}\;\rm m/s^2$$ And, $$a_y=\dfrac{\sum F_{y }}{m}=\dfrac{2.82-3\cos20^\circ}{2}=\color{red}{\bf 0}\;\rm m/s^2$$ b) We need to analyze the $\bf vertical$ 2-N force into its $x$ and $y$ components. From the geometry of the given figure, their components are $$F_{x }=2\sin15^\circ{\;\rm N},\;\;\;\;\;\;\;\;\;F_{y}=2\cos 15^\circ{\;\rm N}$$ Now we need to analyze the $\bf horizontal$ 2-N force into its $x$ and $y$ components. From the geometry of the given figure, their components are $$F_{x }=2\cos15^\circ{\;\rm N},\;\;\;\;\;\;\;\;\;F_{y}=2\sin 15^\circ{\;\rm N}$$ Thus, $$a_x=\dfrac{\sum F_{x }}{m}=\dfrac{2\cos 15^\circ+2\sin15^\circ -3}{2}=\color{red}{\bf -0.275}\;\rm m/s^2$$ And, $$a_y=\dfrac{\sum F_{y }}{m}=\dfrac{1.414+2\sin15^\circ- 2\cos15^\circ}{2}=\color{red}{\bf 0}\;\rm m/s^2$$
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