CAIE FP2 2011 November — Question 10 EITHER

Exam BoardCAIE
ModuleFP2 (Further Pure Mathematics 2)
Year2011
SessionNovember
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicMoments
TypeRod with end on ground or wall supported by string
DifficultyChallenging +1.2 This is a standard Further Maths mechanics problem involving moments, friction, and resolution of forces. While it requires multiple steps (resolving forces, taking moments, geometric relationships), the techniques are routine for FM students. The inequality proof and subsequent calculations with specific conditions are methodical rather than requiring novel insight. Slightly above average difficulty due to the algebraic manipulation and multi-part nature, but well within expected FM mechanics scope.
Spec3.03t Coefficient of friction: F <= mu*R model3.03u Static equilibrium: on rough surfaces3.04b Equilibrium: zero resultant moment and force

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A uniform rod \(A B\), of weight \(W\) and length \(2 a\), rests with the end \(A\) on a rough horizontal plane. A light inextensible string \(B C\) is attached to the rod at \(B\) and passes over a small smooth fixed peg \(P\), which is at a distance \(h\) vertically above \(A\). A particle is attached at \(C\) and hangs vertically. The points \(A , B\) and \(C\) are all in the same vertical plane. In equilibrium the rod is inclined at an angle \(\theta\) to the horizontal (see diagram). The coefficient of friction between the rod and the plane is \(\mu\). Show that $$\mu \geqslant \frac { 2 a \cos \theta } { h + 2 a \sin \theta }$$ Given that the particle attached at \(C\) has weight \(k W\), angle \(A B P = 90 ^ { \circ }\) and \(h = 3 a\), find
  1. the value of \(k\),
  2. the horizontal component of the force on \(P\), in terms of \(W\).

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A uniform rod $A B$, of weight $W$ and length $2 a$, rests with the end $A$ on a rough horizontal plane. A light inextensible string $B C$ is attached to the rod at $B$ and passes over a small smooth fixed peg $P$, which is at a distance $h$ vertically above $A$. A particle is attached at $C$ and hangs vertically. The points $A , B$ and $C$ are all in the same vertical plane. In equilibrium the rod is inclined at an angle $\theta$ to the horizontal (see diagram). The coefficient of friction between the rod and the plane is $\mu$. Show that

$$\mu \geqslant \frac { 2 a \cos \theta } { h + 2 a \sin \theta }$$

Given that the particle attached at $C$ has weight $k W$, angle $A B P = 90 ^ { \circ }$ and $h = 3 a$, find\\
(i) the value of $k$,\\
(ii) the horizontal component of the force on $P$, in terms of $W$.

\hfill \mbox{\textit{CAIE FP2 2011 Q10 EITHER}}