Question

A body is in equilibrium under the action of three coplanar forces $P$, $Q$ and $R$ as shown in the figure. Select the correct statement.

• A. $\frac{P}{\cos \alpha }=\frac{Q}{\cos \beta }=\frac{R}{\cos \gamma }$
• B. $\frac{P}{\sin \beta }=\frac{Q}{\sin \gamma }=\frac{R}{\sin \alpha }$
• C. $\frac{P}{\sin \alpha }=\frac{Q}{\sin \beta }=\frac{R}{\sin \gamma }$
• D. $\frac{P}{\tan \alpha }=\frac{Q}{\tan \beta }=\frac{R}{\tan \gamma }$

Answer 1

The correct option is C $\frac{P}{\sin \alpha }=\frac{Q}{\sin \beta }=\frac{R}{\sin \gamma }$

According to Lami’s theorem,
$\frac{P}{\sin \alpha }=\frac{Q}{\sin \beta }=\frac{R}{\sin \gamma }$
Therefore, correct option is (A).