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 4.6 - Moment of a Couple - Problems - Page 161: 69

Answer

$$ \begin{aligned} & F=75 \mathrm{~N} \\ & P=100 \mathrm{~N} \end{aligned} $$

Work Step by Step

$$ B A=0.5 \mathrm{~m} $$ The couple created by the $150-\mathrm{N}$ forces is $$ M_{C 1}=150(0.5)=75 \mathrm{~N} \cdot \mathrm{m} $$ Then $$ \begin{aligned} \mathbf{M}_{C 1} & =75\left(\frac{3}{5}\right) \mathbf{j}+75\left(\frac{4}{5}\right) \mathbf{k} \\ & =45 \mathbf{j}+60 \mathbf{k} \\ \mathbf{M}_{C 2} & =-P(0.6) \mathbf{k} \\ \mathbf{M}_{C 3} & =-F(0.6) \mathbf{j} \end{aligned} $$ Require $$ \begin{aligned} & \mathbf{M}_{C 1}+\mathbf{M}_{C 2}+\mathbf{M}_{C 3}=\mathbf{0} \\ & 45 \mathbf{j}+60 \mathbf{k}-P(0.6) \mathbf{k}-F(0.6) \mathbf{j}=\mathbf{0} \end{aligned} $$ Equate the $\mathbf{j}$ and $\mathbf{k}$ components $$ \begin{aligned} & 45-F(0.6)=0 \\ & F=75 \mathrm{~N} \\ & 60-P(0.6)=0 \\ & P=100 \mathrm{~N} \end{aligned} $$
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