SPS SPS FM Mechanics (SPS FM Mechanics) 2026 January

2. \begin{figure}[h] \end{figure} The uniform L-shaped lamina \(O A B C D E\), shown in Figure 2, is made from two identical rectangles. Each rectangle is 4 metres long and \(a\) metres wide. Giving each answer in terms of \(a\), find the distance of the centre of mass of the lamina from

1. \(O E\),
2. \(O A\). The lamina is freely suspended from \(O\) and hangs in equilibrium with \(O E\) at an angle \(\theta\) to the downward vertical through \(O\), where \(\tan \theta = \frac { 4 } { 3 }\).
3. Find the value of \(a\).
   [0pt] [Question 2 Continued]

3.
\includegraphics[max width=\textwidth, alt={}, center]{b3e54459-0d05-4858-8978-60fe3d4d1719-06_534_533_191_717} A light elastic string has natural length \(8 a\) and modulus of elasticity \(5 m g\). A particle \(P\) of mass \(m\) is attached to the midpoint of the string. The ends of the string are attached to points \(A\) and \(B\) which are a distance \(12 a\) apart on a smooth horizontal table. The particle \(P\) is held on the table so that \(A P = B P = L\) (see diagram). The particle \(P\) is released from rest. When \(P\) is at the midpoint of \(A B\) it has speed \(\sqrt { 80 a g }\).

1. Find \(L\) in terms of \(a\).
2. Find the initial acceleration of \(P\) in terms of \(g\).
   [0pt] [Question 3 Continued] \section*{4.} A hollow hemispherical bowl of radius \(a\) has a smooth inner surface and is fixed with its axis vertical. A particle \(P\) of mass \(m\) moves in horizontal circles on the inner surface of the bowl, at a height \(x\) above the lowest point of the bowl. The speed of \(P\) is \(\sqrt { \frac { 8 } { 3 } g a }\). Find \(x\) in terms of \(a\).
   [0pt] [Question 4 Continued]

5.
\includegraphics[max width=\textwidth, alt={}, center]{b3e54459-0d05-4858-8978-60fe3d4d1719-10_478_828_178_575}
\(A B\) and \(B C\) are two fixed smooth vertical barriers on a smooth horizontal surface, with angle \(A B C = 60 ^ { \circ }\). A particle of mass \(m\) is moving with speed \(u\) on the surface. The particle strikes \(A B\) at an angle \(\theta\) with \(A B\). It then strikes \(B C\) and rebounds at an angle \(\beta\) with \(B C\) (see diagram). The coefficient of restitution between the particle and each barrier is \(e\) and \(\tan \theta = 2\). The kinetic energy of the particle after the first collision is \(40 \%\) of its kinetic energy before the first collision.

1. Find the value of \(e\).
2. Find the size of angle \(\beta\).
   [0pt] [Question 5 Continued] \section*{6.}
   \includegraphics[max width=\textwidth, alt={}]{b3e54459-0d05-4858-8978-60fe3d4d1719-12_511_1145_296_452}
   A particle \(P\) of mass 0.05 kg is attached to one end of a light inextensible string of length 1 m . The other end of the string is attached to a fixed point \(O\). A particle \(Q\) of mass 0.04 kg is attached to one end of a second light inextensible string. The other end of this string is attached to \(P\). The particle \(P\) moves in a horizontal circle of radius 0.8 m with angular speed \(\omega \operatorname { rad~s } ^ { - 1 }\). The particle \(Q\) moves in a horizontal circle of radius 1.4 m also with angular speed \(\omega \mathrm { rad } \mathrm { s } ^ { - 1 }\). The centres of the circles are vertically below \(O\), and \(O , P\) and \(Q\) are always in the same vertical plane. The strings \(O P\) and \(P Q\) remain at constant angles \(\alpha\) and \(\beta\) respectively to the vertical (see diagram).
3. Find the tension in the string \(O P\).
4. Find the value of \(\omega\).
5. Find the value of \(\beta\).
   [0pt] [Question 6 Continued]

7.
\includegraphics[max width=\textwidth, alt={}, center]{b3e54459-0d05-4858-8978-60fe3d4d1719-14_371_880_191_589} Two uniform smooth spheres \(A\) and \(B\) of equal radii have masses \(m\) and \(\frac { 1 } { 2 } m\) respectively. The two spheres are moving on a horizontal surface when they collide. Immediately before the collision, sphere \(A\) is travelling with speed \(u\) and its direction of motion makes an angle \(\alpha\) with the line of centres. Sphere \(B\) is travelling with speed \(2 u\) and its direction of motion makes an angle \(\beta\) with the line of centres (see diagram). The coefficient of restitution between the spheres is \(\frac { 5 } { 8 }\) and \(\alpha + \beta = 90 ^ { \circ }\).

1. Find the component of the velocity of \(B\) parallel to the line of centres after the collision, giving your answer in terms of \(u\) and \(\alpha\). The direction of motion of \(B\) after the collision is parallel to the direction of motion of \(A\) before the collision.
2. Find the value of \(\tan \alpha\).
   [0pt] [Question 7 Continued]

8. \begin{figure}[h] \end{figure} A smooth solid hemisphere is fixed with its flat surface in contact with rough horizontal ground. The hemisphere has centre \(O\) and radius \(5 a\).
A uniform rod \(A B\), of length \(16 a\) and weight \(W\), rests in equilibrium on the hemisphere with end \(A\) on the ground. The rod rests on the hemisphere at the point \(C\), where \(A C = 12 a\) and angle \(C A O = \alpha\), as shown in Figure 1. Points \(A , C , B\) and \(O\) all lie in the same vertical plane.

1. Explain why \(A O = 13 a\) The normal reaction on the rod at \(C\) has magnitude \(k W\)
2. Show that \(k = \frac { 8 } { 13 }\) The resultant force acting on the rod at \(A\) has magnitude \(R\) and acts upwards at \(\theta ^ { \circ }\) to the horizontal.
3. Find
   1. an expression for \(R\) in terms of \(W\)
   2. the value of \(\theta\)
      (8)
      [0pt] [Question 8 Continued] Spare space for extra working Spare space for extra working Spare space for extra working