Engineering Mechanics: Statics & Dynamics (14th Edition)

Published by Pearson
ISBN 10: 0133915425
ISBN 13: 978-0-13391-542-6

Chapter 4 - Force System Resultants - Section 4.7 - Simplification of a Force and Couple System - Problems - Page 174: 102

Answer

$\begin{aligned} & F_R=1.30 \mathrm{kN} \\ & \theta=86.7^{\circ} \\ & \left(M_R\right)_A=1.02 \mathrm{kN} \cdot \mathrm{m} \text { (counterclockwise) }\end{aligned}$

Work Step by Step

Equivalent Resultant Force And Couple Moment at Point $\boldsymbol{A}$. $ \begin{aligned} \stackrel{ \pm}{\rightarrow}\left(F_R\right)_x=\Sigma F_x ; \quad\left(F_R\right)_x & \\=650 \sin 30^{\circ}-500 \cos 60^{\circ}=75 \mathrm{~N} \rightarrow \\ +\uparrow\left(F_R\right)_y=\Sigma F_y ; \quad\left(F_R\right)_y & \\=-650 \cos 30^{\circ}-300-500 \sin 60^{\circ} \\ & =-1295.93 \mathrm{~N}\\=1295.93 \mathrm{~N} \downarrow \end{aligned} $ As indicated in Fig. $ F_R=\sqrt{\left(F_R\right)_x^2+\left(F_R\right)_y^2}=\sqrt{75^2+1295.93^2}=1298.10 \mathrm{~N}=1.30 \mathrm{kN} \text { } $ $ \theta=\tan ^{-1}\left[\frac{\left(F_R\right)_y}{\left(F_R\right)_x}\right]=\tan ^{-1}\left(\frac{1295.93}{75}\right)=86.69^{\circ}=86.7^{\circ} \quad \text { } $ Also, $ \begin{aligned} ↺+\left(M_R\right)_A=\Sigma M_A ; \quad\left(M_R\right)_A & \\=650 \cos 30^{\circ}(3)+1500-500 \sin 60^{\circ}(5) \\ =1023.69 \mathrm{~N} \cdot \mathrm{m} \\ =1.02 \mathrm{kN} \cdot \mathrm{m} \text { (counter clockwise) } \end{aligned} $
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