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 4.9 - Reduction of a Simple Distributed Loaded - Problems - Page 199: 154

Answer

$\begin{aligned} & F_R=12.0 \mathrm{kN} \\ & \theta=48.4^{\circ} \\ & d=3.28 \mathrm{~m}\end{aligned}$

Work Step by Step

Equivalent Resultant Force. Summing the forces along the $x$ and $y$ axes, $ \begin{array}{ll} \stackrel{+}{\rightarrow}\left(F_R\right)_x=\Sigma F_x ; & \left(F_R\right)_x=-2(4)=-8 \mathrm{kN}=8 \mathrm{kN} \leftarrow \\ +\uparrow\left(F_R\right)_y=\Sigma F_y ; & \left(F_R\right)_y=-3(3)=-9 \mathrm{kN}=9 \mathrm{kN} \downarrow \end{array} $ Then $ F_K=\sqrt{\left(F_R\right)_x^2+\left(F_R\right)_y^2}=\sqrt{8^2+9^2}=12.04 \mathrm{kN}=12.0 \mathrm{kN} $ And $ \theta=\tan ^{-1}\left[\frac{\left(F_R\right)_y}{\left(F_R\right)_s}\right]=\tan ^{-1}\left(\frac{9}{8}\right)=48.37^{\circ}=48.4^{\circ} $ Location of the Resultant Force. Summing the moments about point $A$, $ \begin{aligned} ↺+\left(M_R\right)_A=\Sigma M_A ; \quad-8 x-9 y & =-3(3)(1.5)-2(4)(2) \\ 8 x+9 y & =29.5 \end{aligned} $ Along $A B, x=0$. Then Eq becomes $ \begin{aligned} 8(0)+9 y & =29.5 \\ y & =3.278 \mathrm{~m} \end{aligned} $ Thus, the inter section point of line of action of $\mathbf{F}_R$ on $A B$ measured to the right from point $A$ is $ d=y=3.28 \mathrm{~m} $
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