| Exam Board | OCR |
|---|---|
| Module | M3 (Mechanics 3) |
| Year | 2008 |
| Session | January |
| Marks | 9 |
| Paper | Download PDF ↗ |
| Mark scheme | Download PDF ↗ |
| Topic | Moments |
| Type | Rod hinged to wall with string support |
| Difficulty | Standard +0.8 This is a two-rod statics problem requiring moment equations about multiple points, resolution of forces at a hinge, and systematic application of equilibrium conditions across connected bodies. While the geometry is given (avoiding trigonometric complexity), students must carefully track forces at joint B and apply moments correctly to both rods, which is more demanding than single-body equilibrium problems typical at this level. |
| Spec | 3.04a Calculate moments: about a point3.04b Equilibrium: zero resultant moment and force |
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Two uniform rods $A B$ and $B C$, each of length 2 m , are freely jointed at $B$. The weights of the rods are $W \mathrm {~N}$ and 50 N respectively. The end $A$ of $A B$ is hinged at a fixed point. The rods $A B$ and $B C$ make angles $\tan ^ { - 1 } \left( \frac { 3 } { 4 } \right)$ and $\beta$ respectively with the downward vertical, and are held in equilibrium in a vertical plane by a horizontal force of magnitude 75 N acting at $C$ (see diagram).\\
(i) By taking moments about $B$ for $B C$, show that $\tan \beta = 3$.\\
(ii) Write down the horizontal and vertical components of the force acting on $A B$ at $B$.\\
(iii) Find the value of $W$.
\hfill \mbox{\textit{OCR M3 2008 Q2 [9]}}