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: 99

Answer

$\begin{aligned} & F_R=5.93 \mathrm{kN} \\ & \theta=77.8^{\circ} P \\ & M_{R_A}=34.8 \mathrm{kN} \cdot \mathrm{m}\end{aligned}$

Work Step by Step

$ \begin{aligned} \pm F_{R_s}=\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_x}^2+F_{R_s}^2}=\sqrt{1.25^2+5.799^2}=5.93 \mathrm{kN} $$ and $ \begin{gathered} \theta=\tan ^{-1}\left(\frac{F_{R_y}}{F_{R_s}}\right)=\tan ^{-1}\left(\frac{5.799}{1.25}\right)=77.8^{\circ} P \\ \mathrm{↺}+M_{R_A}=\Sigma M_A ; \quad M_{R_A}=-2.5\left(\frac{3}{5}\right)(2)-1.5 \cos 30^{\circ}(6)-3(8) \\ =-34.8 \mathrm{kN} \cdot \mathrm{m}=34.8 \mathrm{kN} \cdot \mathrm{m} \quad(\text { Clockwise }) \end{gathered}
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