| Exam Board | WJEC |
|---|---|
| Module | Unit 4 (Unit 4) |
| Year | 2019 |
| Session | June |
| Marks | 6 |
| Paper | Download PDF ↗ |
| Mark scheme | Download PDF ↗ |
| Topic | Forces, equilibrium and resultants |
| Type | Resultant of coplanar forces |
| Difficulty | Moderate -0.8 This is a straightforward mechanics question requiring resolution of forces in two perpendicular directions and use of Pythagoras. Part (a) involves standard trigonometry (finding sin α and cos α from tan α) and vector addition—routine A-level mechanics. Part (b) requires only the simple observation that three forces with magnitudes 21, 11, and 8 cannot form a triangle (21 > 11 + 8), making it easier than average overall. |
| Spec | 3.03e Resolve forces: two dimensions3.03m Equilibrium: sum of resolved forces = 03.03p Resultant forces: using vectors |
Three coplanar horizontal forces of magnitude $21$ N, $11$ N and $8$ N act on a particle $P$ in the directions shown in the diagram.
\includegraphics{figure_7}
\begin{enumerate}[label=(\alph*)]
\item Given that $\tan\alpha = \frac{3}{4}$, calculate the magnitude of the resultant force. [5]
\item Explain why the forces cannot be in equilibrium whatever the value of $\alpha$. [1]
\end{enumerate}
\hfill \mbox{\textit{WJEC Unit 4 2019 Q7 [6]}}