Engineering Mechanics: Statics & Dynamics (14th Edition)

Published by Pearson
ISBN 10: 0133915425
ISBN 13: 978-0-13391-542-6

Chapter 16 - Planar Kinematics of a Rigid Body - Section 16.3 - Rotation about a Fixed Axis - Problems - Page 337: 35

Answer

Ans: $$ \begin{aligned} & \mathbf{v}_C=\{-4.8 \mathbf{i}-3.6 \mathbf{j}-1.2 \mathbf{k}\} \mathrm{m} / \mathrm{s} \\ & \mathbf{a}_C=\{38.4 \mathbf{i}-64.8 \mathbf{j}+40.8 \mathbf{k}\} \mathrm{m} / \mathrm{s}^2 \end{aligned} $$

Work Step by Step

We need to express $w$ of the plate in vectorial form The unit vector that defined the direction of $\omega$ is? $$ \mathbf{u}_{O A}=\frac{-0.3 \mathbf{i}+0.2 \mathbf{j}+0.6 \mathbf{k}}{\sqrt{(-0.3)^2+0.2^2+0.6^2}}=-\frac{3}{7} \mathbf{i}+\frac{2}{7} \mathbf{j}+\frac{6}{7} \mathbf{k} $$ Then: $$ \begin{aligned} & \omega=\omega \mathbf{u}_{O A}=14\left(-\frac{3}{7} \mathbf{i}+\frac{2}{7} \mathbf{j}+\frac{6}{7} \mathbf{k}\right)=[-6 \mathbf{i}+4 \mathbf{j}+12 \mathbf{k}] \mathrm{rad} / \mathrm{s} \\ & \omega=\operatorname{cte}, \alpha=0 \\ & r_c=[-0.3 \mathbf{i}+0.4 \mathbf{j}] \mathrm{m} \end{aligned} $$ $$ \begin{aligned} \mathbf{v}_C & =\omega \times \mathbf{r}_C \\ & =(-6 \mathbf{i}+4 \mathbf{j}+12 \mathbf{k}) \times(-0.3 \mathbf{i}+0.4 \mathbf{j}) \\ & =[-4.8 \mathbf{i}-3.6 \mathbf{j}-1.2 \mathbf{k}] \mathrm{m} / \mathrm{s} \end{aligned} $$ So: $$ \begin{aligned} \mathbf{a}_C & =\alpha \times \mathbf{r}_C+\omega \times\left(\boldsymbol{\omega} \times \mathbf{r}_C\right) \\ & =0+(-6 \mathbf{i}+4 \mathbf{j}+12 \mathbf{k}) \times[(-6 \mathbf{i}+4 \mathbf{j}+12 \mathbf{k}) \times(-0.3 \mathbf{i}+0.4 \mathbf{j})] \\ & =[38.4 \mathbf{i}-64.8 \mathbf{j}+40.8 \mathbf{k}] \mathrm{m} / \mathrm{s}^2 \end{aligned} $$
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