Fundamentals of Physics Extended (10th Edition)

Published by Wiley
ISBN 10: 1-11823-072-8
ISBN 13: 978-1-11823-072-5

Chapter 6 - Force and Motion-II - Problems - Page 147: 88

Answer

$$ T=9.4 \mathrm{N} $$

Work Step by Step

For the $m_{2}=1.0$ kg block, application of Newton's laws result in $$ \begin{array}{rl}{F \cos \theta-T-f_{k}=m_{2} a} & {x \text { axis }} \\ {F_{N}-F \sin \theta-m_{2} g=0} & {y \text { axis }}\end{array} $$ since $f_{k}=\mu_{k} F_{N},$ these equations can be combined into an equation to solve for $a :$ $$ F\left(\cos \theta-\mu_{k} \sin \theta\right)-T-\mu_{k} m_{2} g=m_{2} a $$ Similarly (but without the applied push) we analyze the $m_{1}=2.0$ kg block: $$\begin{array}{rlrl}{T-f_{k}^{\prime}} & {=m_{1} a} & {} & {x \text { axis }} \\ {F_{N}^{\prime}-m_{1} g} & {=0} & {} & {y \text { axis }}\end{array}$$ Using $f_{k}=\mu_{k} F_{N}^{\prime},$ the equations can be combined: $$ T-\mu_{k} m_{1} g=m_{1} a $$ Subtracting the two equations for $a$ and solving for the tension, we obtain $$ T=\frac{m_{1}\left(\cos \theta-\mu_{k} \sin \theta\right)}{m_{1}+m_{2}} F=\frac{(2.0 \mathrm{kg})\left[\cos 35^{\circ}-(0.20) \sin 35^{\circ}\right]}{2.0 \mathrm{kg}+1.0 \mathrm{kg}}(20 \mathrm{N})$$$$=9.4 \mathrm{N} $$
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