Three coplanar forces of magnitudes 20 N, 100 N and \(F\) N act at a point. The directions of these forces are shown in the diagram.
Given that the three forces are in equilibrium, find \(F\) and \(\alpha\).
Solution
To solve for \(F\) and \(\alpha\), we use the equilibrium condition, which states that the sum of the forces in any direction must be zero.
Resolve horizontally:
\(F \cos \alpha - 20 \cos 40 - 100 \sin 20 = 0\)
\(F \cos \alpha = 49.5229 \ldots\)
Resolve vertically:
\(F \sin \alpha + 20 \sin 40 - 100 \cos 20 = 0\)
\(F \sin \alpha = 81.1135 \ldots\)
Now, solve for \(F\):
\(F = \sqrt{(49.5229 \ldots)^2 + (81.1135 \ldots)^2}\)
\(F = 95.0\)
To find \(\alpha\):
\(\tan \alpha = \frac{81.1135 \ldots}{49.5229 \ldots}\)
\(\alpha = 58.6\)
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