Fundamentals of Physics Extended (10th Edition)

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

Chapter 12 - Equilibrium and Elasticity - Problems - Page 347: 24

Answer

$$1.19$$

Work Step by Step

At the static equilibrium, the net force acting on the the climber zero. Therefore, at horizontal equilibrium: $F_N-T\sin\phi=0\implies F_N=T\sin\phi\;........(1)$ at vertical equilibrium: $f_s+T\cos\phi-W=0\;...............(2)$ The net torque about the contact point between the wall and her feet and is also zero. $WL\sin\theta-TL\sin(180^{\circ}-\theta-\phi)=0$ or, $T=\frac{W\sin\theta}{\sin(180^{\circ}-\theta-\phi)}\;...........(3)$ Again, $f_s=\mu_sF_N$ or, $f_s=\mu_sT\sin\phi$ Substituting in Eq. $2$, we obtain $\mu_sT\sin\phi+T\cos\phi-W=0$ or, $T(\mu_s\sin\phi+\cos\phi)=W$ Using Eq. $3$, we obtain $\frac{W\sin\theta}{\sin(180^{\circ}-\theta-\phi)}(\mu_s\sin\phi+\cos\phi)=W$ or, $\mu_s=\frac{1}{\sin\phi}\Big(\frac{\sin(180^{\circ}-\theta-\phi)}{\sin\theta}-\cos\phi\Big)$ Substituting the given values, we obtain $\mu_s=\frac{1}{\sin30^{\circ}}\Big(\frac{\sin(180^{\circ}-40^{\circ}-30^{\circ})}{\sin40^{\circ}}-\cos30^{\circ}\Big)$ or, $\boxed{\mu_s=1.19}$ Therefore, the coefficient of static friction between her climbing shoes and the wall is $1.19$
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