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: 100

Answer

$\begin{aligned} & F_R=5.93 \mathrm{kN} \\ & \theta=77.8^{\circ} \\ & M_B=11.6 \mathrm{kN} \cdot \mathrm{m} \text { (Counterclockwise) }\end{aligned}$

Work Step by Step

$ \begin{aligned} & \stackrel{\Rightarrow}{\Rightarrow} F_{R_x}=\Sigma F_x ; \quad F_{R_x}=1.5 \sin 30^{\circ}-2.5\left(\frac{4}{5}\right) \\ & =-1.25 \mathrm{kN}=1.25 \mathrm{kN} \leftarrow \\ & +\uparrow F_{R_y}=\Sigma F_y ; \quad F_{R_y}=-1.5 \cos 30^{\circ}-2.5\left(\frac{3}{5}\right)-3 \\ & =-5.799 \mathrm{kN}=5.799 \mathrm{kN} \downarrow \\ & \end{aligned} $ Thus, $ F_R=\sqrt{F_{R_s}^2+F_{R_y}^2}=\sqrt{1.25^2+5.799^2}=5.93 \mathrm{kN} $ and $ \theta=\tan ^{-1}\left(\frac{F_{R_y}}{F_{R_x}}\right)=\tan ^{-1}\left(\frac{5.799}{1.25}\right)=77.8^{\circ} $ $ \begin{aligned} ↺+M_{R_a}=\Sigma M_{R_a} ; \quad & M_B=1.5 \cos 30^{\circ}(2)+2.5\left(\frac{3}{5}\right)(6) \\ & =11.6 \mathrm{kN} \cdot \mathrm{m} \quad \text { (Counterclockwise) } \end{aligned} $
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