Authors: Russell C. Hibbeler
ISBN-13: 978-0133915426
See our solution for Question 28FP from Chapter 2 from Hibbeler's Engineering Mechanics.
We are given the force $F = 650\;{\rm{N}}$.
We are asked to determine the projected component of the force along the line OA.
The following is the diagram to calculate the projected component of the force.

To find the unit vector we will use the formula,
\[\begin{array}{l} \vec u = \left( {\frac{{12}}{{13}}\hat i + \frac{5}{{13}}\hat j} \right)\\ \vec u = \left( {0.923\hat i + 0.385\hat j} \right) \end{array}\]To find the projected component of force we will use,
\[\vec F = F \cdot \vec u\]On plugging the known values in the above relation, we get,
\[\begin{array}{l} \vec F = \left( {0\hat i + 650\;{\rm{N}}\hat j} \right) \cdot \left( {0.923\hat i + 0.385\hat j} \right)\\ \vec F = 250.25\;{\rm{N}} \end{array}\]To find the projection of the force we will use the following relation,
\[{F_{OA}} = \vec F\vec u\]On plugging the known values in the above relation, we get,
\[\begin{array}{l} {F_{OA}} = \left( {250.25\;{\rm{N}}} \right) \cdot \left( {0.923\hat i + 0.385\hat j} \right)\\ {F_{OA}} = \left( {230.9\hat i + 96.3\hat j} \right)\;{\rm{N}} \end{array}\]