OCR M2 2010 January — Question 3 8 marks

Exam BoardOCR
ModuleM2 (Mechanics 2)
Year2010
SessionJanuary
Marks8
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicCentre of Mass 1
TypeConical or hemispherical shell composite
DifficultyStandard +0.3 This is a standard M2 centre of mass question requiring knowledge of standard results (cone CM at h/3 from base), straightforward composite body calculation using moments, and basic equilibrium with resolved forces. The 'show that' in part (i) guides students to the answer, and part (ii) is routine resolution of forces. Slightly above average difficulty due to 3D geometry visualization and two-part structure, but uses well-practiced techniques with no novel insight required.
Spec6.04b Find centre of mass: using symmetry6.04c Composite bodies: centre of mass6.04e Rigid body equilibrium: coplanar forces

3 \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{8e1225a2-cb98-4b71-a4af-0150f093f852-2_528_688_845_731} \captionsetup{labelformat=empty} \caption{Fig. 1}
\end{figure} A uniform conical shell has mass 0.2 kg , height 0.3 m and base diameter 0.8 m . A uniform hollow cylinder has mass 0.3 kg , length 0.7 m and diameter 0.8 m . The conical shell is attached to the cylinder, with the circumference of its base coinciding with one end of the cylinder (see Fig. 1).
  1. Show that the distance of the centre of mass of the combined object from the vertex of the conical shell is 0.47 m . \begin{figure}[h]
    \includegraphics[alt={},max width=\textwidth]{8e1225a2-cb98-4b71-a4af-0150f093f852-2_497_572_1836_788} \captionsetup{labelformat=empty} \caption{Fig. 2}
    \end{figure} The combined object is freely suspended from its vertex and is held with its axis horizontal. This is achieved by means of a wire attached to a point on the circumference of the base of the conical shell. The wire makes an angle of \(80 ^ { \circ }\) with the slant edge of the conical shell (see Fig. 2).
  2. Calculate the tension in the wire.

3

\begin{figure}[h]
\begin{center}
  \includegraphics[alt={},max width=\textwidth]{8e1225a2-cb98-4b71-a4af-0150f093f852-2_528_688_845_731}
\captionsetup{labelformat=empty}
\caption{Fig. 1}
\end{center}
\end{figure}

A uniform conical shell has mass 0.2 kg , height 0.3 m and base diameter 0.8 m . A uniform hollow cylinder has mass 0.3 kg , length 0.7 m and diameter 0.8 m . The conical shell is attached to the cylinder, with the circumference of its base coinciding with one end of the cylinder (see Fig. 1).\\
(i) Show that the distance of the centre of mass of the combined object from the vertex of the conical shell is 0.47 m .

\begin{figure}[h]
\begin{center}
  \includegraphics[alt={},max width=\textwidth]{8e1225a2-cb98-4b71-a4af-0150f093f852-2_497_572_1836_788}
\captionsetup{labelformat=empty}
\caption{Fig. 2}
\end{center}
\end{figure}

The combined object is freely suspended from its vertex and is held with its axis horizontal. This is achieved by means of a wire attached to a point on the circumference of the base of the conical shell. The wire makes an angle of $80 ^ { \circ }$ with the slant edge of the conical shell (see Fig. 2).\\
(ii) Calculate the tension in the wire.

\hfill \mbox{\textit{OCR M2 2010 Q3 [8]}}