Edexcel M2 2016 June — Question 5 11 marks

Exam BoardEdexcel
ModuleM2 (Mechanics 2)
Year2016
SessionJune
Marks11
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicMoments
TypeRod with end on ground or wall supported by string
DifficultyStandard +0.8 This is a challenging M2 ladder problem requiring resolution of forces in two directions, taking moments about a strategic point, and applying limiting equilibrium conditions. The non-standard geometry (rod against vertical wall rather than floor, with string attachment) and the need to find three interconnected quantities including the direction of the resultant force makes this harder than typical ladder problems, though still within standard M2 scope.
Spec3.03t Coefficient of friction: F <= mu*R model6.04e Rigid body equilibrium: coplanar forces

5. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{790546bf-38a4-4eb7-876e-941fe58f4a48-09_952_664_246_712} \captionsetup{labelformat=empty} \caption{Figure 3}
\end{figure} A uniform rod \(A B\) has mass 6 kg and length 2 m . The end \(A\) of the rod rests against a rough vertical wall. One end of a light string is attached to the rod at \(B\). The other end of the string is attached to the wall at \(C\), which is vertically above \(A\). The angle between the rod and the string is \(30 ^ { \circ }\) and the angle between the rod and the wall is \(70 ^ { \circ }\), as shown in Figure 3. The rod is in a vertical plane perpendicular to the wall and rests in limiting equilibrium. Find
  1. the tension in the string,
  2. the coefficient of friction between the rod and the wall,
  3. the direction of the force exerted on the rod by the wall at \(A\).
    DO NOT WIRITE IN THIS AREA

5a
AnswerMarks
Moments about \(A\): \(6g(\times 1) \times \sin 70 = T \sin 30 \times 2\)M1A2
\(T = 55.3\)(N) or 55 (N)A1 (4)
Notes: First M1 for a complete method to find \(T\), with usual rules, correct no. of terms, allow sin/cos confusion, dim correct (missing \(g\) is an A error) and allow incorrect angles; First A2 for a correct equation (A1A0 for one error); Third A1 for 55 (N) or 55.3 (N)
5b
AnswerMarks Guidance
Resolve horizontally: \(T \cos 50 = R(= 35.5)\)B1 ft
Resolve vertically: \(T \sin 50 = 6g \pm F\)M1A1 ft
\(\F\ = 16.5\) (16.473...)
Use \(F = \mu R\): \(\mu = \frac{6g - T \sin 50}{T \cos 50}\) (with their values)M1
\(= 0.464\) or 0.46A1 (5)
Notes: First B1 ft for resolving horizontally (\(T\) does not need to be substituted); First M1 for resolving vertically with usual rules, must be using 40⁰ or 50⁰; First A1 ft for a correct equation (\(T\) does not need to be substituted); Second M1, independent, for use of \(F = \mu R\), must have found an \(F\) and an \(R\); Second A1 for 0.46 or 0.464; N.B. They may resolve in other directions e.g. along the rod or perpendicular to the rod or take moments e.g. about \(B\) or \(C\)
5c
AnswerMarks
Use of tan and their components: \(\tan^{-1}\left(\frac{35.5}{16.5}\right)\)M1
\(= 65.1°\) or 65⁰ to the upward vertical or equivalent (24.9⁰ or 25⁰ above the horizontal)A1 (2) [11]
Notes: First M1 for a complete method to find the angle (must have found the two components) with either the horizontal or vertical; First A1 for 65⁰ or 65.1⁰ to the upward vertical oe (A0 for just an angle) or the angle marked on a clear diagram with an arrow.
## 5a
| Moments about $A$: $6g(\times 1) \times \sin 70 = T \sin 30 \times 2$ | M1A2 |
| $T = 55.3$(N) or 55 (N) | A1 (4) |
| **Notes:** First M1 for a complete method to find $T$, with usual rules, correct no. of terms, allow sin/cos confusion, dim correct (missing $g$ is an A error) and allow incorrect angles; First A2 for a correct equation (A1A0 for one error); Third A1 for 55 (N) or 55.3 (N) |

## 5b
| Resolve horizontally: $T \cos 50 = R(= 35.5)$ | B1 ft |
| Resolve vertically: $T \sin 50 = 6g \pm F$ | M1A1 ft |
| $\|F\| = 16.5$ (16.473...) | |
| Use $F = \mu R$: $\mu = \frac{6g - T \sin 50}{T \cos 50}$ (with their values) | M1 |
| $= 0.464$ or 0.46 | A1 (5) |
| **Notes:** First B1 ft for resolving horizontally ($T$ does not need to be substituted); First M1 for resolving vertically with usual rules, must be using 40⁰ or 50⁰; First A1 ft for a correct equation ($T$ does not need to be substituted); Second M1, independent, for use of $F = \mu R$, must have found an $F$ and an $R$; Second A1 for 0.46 or 0.464; N.B. They may resolve in other directions e.g. along the rod or perpendicular to the rod or take moments e.g. about $B$ or $C$ |

## 5c
| Use of tan and their components: $\tan^{-1}\left(\frac{35.5}{16.5}\right)$ | M1 |
| $= 65.1°$ or 65⁰ to the upward vertical or equivalent (24.9⁰ or 25⁰ above the horizontal) | A1 (2) [11] |
| **Notes:** First M1 for a complete method to find the angle (must have found the two components) with either the horizontal or vertical; First A1 for 65⁰ or 65.1⁰ to the upward vertical oe (A0 for just an angle) or the angle marked on a clear diagram with an arrow. |

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5.

\begin{figure}[h]
\begin{center}
  \includegraphics[alt={},max width=\textwidth]{790546bf-38a4-4eb7-876e-941fe58f4a48-09_952_664_246_712}
\captionsetup{labelformat=empty}
\caption{Figure 3}
\end{center}
\end{figure}

A uniform rod $A B$ has mass 6 kg and length 2 m . The end $A$ of the rod rests against a rough vertical wall. One end of a light string is attached to the rod at $B$. The other end of the string is attached to the wall at $C$, which is vertically above $A$. The angle between the rod and the string is $30 ^ { \circ }$ and the angle between the rod and the wall is $70 ^ { \circ }$, as shown in Figure 3. The rod is in a vertical plane perpendicular to the wall and rests in limiting equilibrium.

Find
\begin{enumerate}[label=(\alph*)]
\item the tension in the string,
\item the coefficient of friction between the rod and the wall,
\item the direction of the force exerted on the rod by the wall at $A$.\\

DO NOT WIRITE IN THIS AREA
\end{enumerate}

\hfill \mbox{\textit{Edexcel M2 2016 Q5 [11]}}