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 352: 73a

Answer

$F = (35~\hat{i}+200~\hat{j})~N$

Work Step by Step

We can find the angle $\theta$ the ladder makes with the ground: $sin~\theta = \frac{8.0~m}{10~m}$ $\theta = sin^{-1}~(\frac{8.0~m}{10~m})$ $\theta = 53.13^{\circ}$ To find $F_w$, the magnitude of the force of the wall on the ladder, we can consider the torque about a rotation axis at the bottom of the ladder: $\sum \tau = 0$ $h~F_w-(5~cos~\theta)~mg - (2.0~sin~\theta)~F = 0$ $h~F_w = (5~cos~\theta)~mg + (2.0~sin~\theta)~F$ $F_w = \frac{(5~cos~\theta)~mg + (2.0~sin~\theta)~F}{h}$ $F_w = \frac{(5~cos~53.13^{\circ})~(200~N) + (2.0~sin~53.13^{\circ})~(50~N)}{8.0~m}$ $F_w = 85~N$ To find the horizontal component of the force on the ladder due to the ground, we can consider the horizontal forces on the ladder: $F_x+50~N-85~N = 0$ $F_x = 85~N - 50~N$ $F_x = 35~N$ The vertical component of the force on the ladder due to the ground is equal in magnitude to the weight of the ladder: $F_y = 200~N$ We can express the force on the ladder due to the ground in unit-vector notation: $F = (35~\hat{i}+200~\hat{j})~N$
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