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 4.8 - Further Simplification of a Force and Couple System - Problems - Page 189: 134

Answer

$$ \begin{aligned} & \mathbf{F}_R=\{141 \mathbf{i}+100 \mathbf{j}+159 \mathbf{k}\} \mathbf{N} \\ & \mathbf{M}_{R_O}=\{122 \mathbf{i}-183 \mathbf{k}\} \mathbf{N} \cdot \mathrm{m} \end{aligned} $$

Work Step by Step

Force And Moment Vectors: $$ \begin{aligned} \mathbf{F}_1 & =\{300 \mathbf{k}\} \mathbf{N} \quad \mathbf{F}_3=\{100 \mathbf{j}\} \mathbf{N} \\ \mathbf{F}_2 & =200\left\{\cos 45^{\circ} \mathbf{i}-\sin 45^{\circ} \mathbf{k}\right\} \mathbf{N} \\ & =\{141.42 \mathbf{i}-141.42 \mathbf{k}\} \mathbf{N} \\ \mathbf{M}_1 & =\{100 \mathbf{k}\} \mathbf{N} \cdot \mathrm{m} \\ \mathbf{M}_2 & =180\left\{\cos 45^{\circ} \mathbf{i}-\sin 45^{\circ} \mathbf{k}\right\} \mathbf{N} \cdot \mathrm{m} \\ & =\{127.28 \mathbf{i}-127.28 \mathbf{k}\} \mathrm{N} \cdot \mathrm{m} \end{aligned} $$ Equivalent Force and Couple Moment At Point O: $$ \begin{aligned} \mathbf{F}_R=\Sigma \mathbf{F} ; \quad \mathbf{F}_R & =\mathbf{F}_1+\mathbf{F}_2+\mathbf{F}_3 \\ & =141.42 \mathbf{i}+100.0 \mathbf{j}+(300-141.42) \mathbf{k} \\ & =\{141 \mathbf{i}+100 \mathbf{j}+159 \mathbf{k}\} \mathbf{N} \end{aligned} $$ The position vectors are $\mathbf{r}_1=\{0.5 \mathbf{j}\} \mathrm{m}$ and $\mathbf{r}_2=\{1.1 \mathbf{j}\} \mathrm{m}$. $$ \begin{aligned} \mathbf{M}_{R_o}=\Sigma \mathbf{M}_o ; \quad \mathbf{M}_{R_o}= & \mathbf{r}_1 \times \mathbf{F}_1+\mathbf{r}_2 \times \mathbf{F}_2+\mathbf{M}_1+\mathbf{M}_2 \\ = & \left|\begin{array}{ccc} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ 0 & 0.5 & 0 \\ 0 & 0 & 300 \end{array}\right| \\ & +\left|\begin{array}{ccc} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ 0 & 1.1 & 0 \\ 141.42 & 0 & -141.42 \end{array}\right| \\ & +100 \mathbf{k}+127.28 \mathbf{i}-127.28 \mathbf{k} \\ = & \{122 \mathbf{i}-183 \mathbf{k}\} \mathrm{N} \cdot \mathrm{m} \end{aligned} $$
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