Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 12 - Rotation of a Rigid Body - Conceptual Questions - Page 347: 8

Answer

$ \tau_f\gt \tau_a=\tau_b\gt \tau_c=\tau_d\gt \tau_f $

Work Step by Step

We know that torque is given by $$\tau=F_{\perp }r$$ where $F_{\perp }$ is the perpendicular force component to $r$. Now we need to find the torque produced by each force around the hang point of the door. $$\tau_a=F\left[\dfrac{L}{2}\right]=\dfrac{FL}{2}$$ $$\tau_b=2F\left[\dfrac{L}{4}\right]=\dfrac{FL}{2}$$ $$\tau_c=F\sin45^\circ\left[\dfrac{L}{2}\right]=F\dfrac{\sqrt2}{2}\dfrac{ L}{2}=\dfrac{\sqrt2 FL}{4}=0.35FL$$ $$\tau_d=F\sin45^\circ\left[\dfrac{L}{2}\right]=F\dfrac{\sqrt2}{2}\dfrac{ L}{2}=\dfrac{\sqrt2 FL}{4}=0.35FL$$ $$\tau_e=2F\left[L\right]=2FL$$ $$\tau_f= F\left[L\right]\sin 0^\circ=0$$ Thus, from above, the rank of the torques is $$\boxed{\tau_f\gt \tau_a=\tau_b\gt \tau_c=\tau_d\gt \tau_f}$$
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