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Edexcel M5 2010 June Q5
15 marks Challenging +1.8
  1. A raindrop falls vertically under gravity through a cloud. In a model of the motion the raindrop is assumed to be spherical at all times and the cloud is assumed to consist of stationary water particles. At time \(t = 0\), the raindrop is at rest and has radius \(a\). As the raindrop falls, water particles from the cloud condense onto it and the radius of the raindrop is assumed to increase at a constant rate \(\lambda\). A time \(t\) the speed of the raindrop is \(v\).
    1. Show that
    $$\frac { \mathrm { d } v } { \mathrm {~d} t } + \frac { 3 \lambda v } { ( \lambda t + a ) } = g$$
  2. Find the speed of the raindrop when its radius is \(3 a\).
Edexcel M5 2010 June Q6
11 marks Challenging +1.8
  1. A uniform circular disc has mass \(m\), centre \(O\) and radius \(2 a\). It is free to rotate about a fixed smooth horizontal axis \(L\) which lies in the same plane as the disc and which is tangential to the disc at the point \(A\). The disc is hanging at rest in equilibrium with \(O\) vertically below \(A\) when it is struck at \(O\) by a particle of mass \(m\). Immediately before the impact the particle is moving perpendicular to the plane of the disc with speed \(3 \sqrt { } ( a g )\). The particle adheres to the disc at \(O\).
    1. Find the angular speed of the disc immediately after the impact.
    2. Find the magnitude of the force exerted on the disc by the axis immediately after the impact.
Edexcel M5 2011 June Q1
4 marks Standard +0.8
  1. A particle moves from the point \(A\) with position vector \(( 3 \mathbf { i } - \mathbf { j } + 3 \mathbf { k } ) \mathrm { m }\) to the point \(B\) with position vector \(( \mathbf { i } - 2 \mathbf { j } - 4 \mathbf { k } ) \mathrm { m }\) under the action of the force \(( 2 \mathbf { i } - 3 \mathbf { j } - \mathbf { k } ) \mathrm { N }\). Find the work done by the force.
    (4)
  2. A particle \(P\) moves in the \(x - y\) plane so that its position vector \(\mathbf { r }\) metres at time \(t\) seconds satisfies the differential equation
$$\frac { \mathrm { d } ^ { 2 } \mathbf { r } } { \mathrm {~d} t ^ { 2 } } - 4 \mathbf { r } = - 3 \mathrm { e } ^ { t } \mathbf { j }$$ When \(t = 0\), the particle is at the origin and is moving with velocity ( \(2 \mathbf { i } + \mathbf { j }\) ) \(\mathrm { ms } ^ { - 1 }\).
Find \(\mathbf { r }\) in terms of \(t\).
Edexcel M5 2011 June Q3
7 marks Challenging +1.2
  1. A rocket propels itself by its engine ejecting burnt fuel. Initially the rocket has total mass \(M\), of which a mass \(k M , k < 1\), is fuel. The rocket is at rest when its engine is started. The burnt fuel is ejected with constant speed \(c\), relative to the rocket, in a direction opposite to that of the rocket's motion. Assuming that there are no external forces, find the speed of the rocket when all its fuel has been burnt.
  2. Two forces \(\mathbf { F } _ { 1 } = ( 3 \mathbf { j } + \mathbf { k } ) \mathrm { N }\) and \(\mathbf { F } _ { 2 } = ( 4 \mathbf { i } + \mathbf { j } - \mathbf { k } ) \mathrm { N }\) act on a rigid body.
The force \(\mathbf { F } _ { 1 }\) acts at the point with position vector ( \(2 \mathbf { i } - \mathbf { j } + 3 \mathbf { k }\) ) m and the force \(\mathbf { F } _ { 2 }\) acts at the point with position vector ( \(- 3 \mathbf { i } + 2 \mathbf { k }\) ) m.
The two forces are equivalent to a single force \(\mathbf { R }\) acting at the point with position vector \(( \mathbf { i } + 2 \mathbf { j } + \mathbf { k } ) \mathrm { m }\) together with a couple of moment \(\mathbf { G }\). Find,
  1. \(\mathbf { R }\),
  2. \(\mathbf { G }\). A third force \(\mathbf { F } _ { 3 }\) is now added to the system. The force \(\mathbf { F } _ { 3 }\) acts at the point with position vector ( \(2 \mathbf { i } - \mathbf { k }\) ) m and the three forces \(\mathbf { F } _ { 1 } , \mathbf { F } _ { 2 }\) and \(\mathbf { F } _ { 3 }\) are equivalent to a couple.
  3. Find the magnitude of the couple.
Edexcel M5 2011 June Q5
8 marks Challenging +1.2
5. A uniform rod \(P Q\), of mass \(m\) and length \(2 a\), is made to rotate in a vertical plane with constant angular speed \(\sqrt { } \left( \frac { g } { a } \right)\) about a fixed smooth horizontal axis through the end \(P\) of the rod. Show that, when the rod is inclined at an angle \(\theta\) to the downward vertical, the magnitude of the force exerted on the axis by the rod is \(2 m g \left| \cos \left( \frac { 1 } { 2 } \theta \right) \right|\).
Edexcel M5 2011 June Q6
7 marks Challenging +1.2
6. A uniform rod \(A B\) of mass \(4 m\) is free to rotate in a vertical plane about a fixed smooth horizontal axis, \(L\), through \(A\). The rod is hanging vertically at rest when it is struck at its end \(B\) by a particle of mass \(m\). The particle is moving with speed \(u\), in a direction which is horizontal and perpendicular to \(L\), and after striking the rod it rebounds in the opposite direction with speed \(v\). The coefficient of restitution between the particle and the rod is 1 . Show that \(u = 7 v\).
Edexcel M5 2011 June Q7
10 marks Challenging +1.8
7. Prove, using integration, that the moment of inertia of a uniform solid right circular cone, of mass \(M\) and base radius \(a\), about its axis is \(\frac { 3 } { 10 } M a ^ { 2 }\).
[0pt] [You may assume, without proof, that the moment of inertia of a uniform circular disc, of mass \(m\) and radius \(r\), about an axis through its centre and perpendicular to its plane is \(\left. \frac { 1 } { 2 } m r ^ { 2 } .\right]\)
Edexcel M5 2011 June Q8
17 marks Challenging +1.2
  1. A pendulum consists of a uniform rod \(P Q\), of mass \(3 m\) and length \(2 a\), which is rigidly fixed at its end \(Q\) to the centre of a uniform circular disc of mass \(m\) and radius \(a\). The rod is perpendicular to the plane of the disc. The pendulum is free to rotate about a fixed smooth horizontal axis \(L\) which passes through the end \(P\) of the rod and is perpendicular to the rod.
    1. Show that the moment of inertia of the pendulum about \(L\) is \(\frac { 33 } { 4 } m a ^ { 2 }\).
    The pendulum is released from rest in the position where \(P Q\) makes an angle \(\alpha\) with the downward vertical. At time \(t , P Q\) makes an angle \(\theta\) with the downward vertical.
  2. Show that the angular speed, \(\dot { \theta }\), of the pendulum satisfies $$\dot { \theta } ^ { 2 } = \frac { 40 g ( \cos \theta - \cos \alpha ) } { 33 a }$$
  3. Hence, or otherwise, find the angular acceleration of the pendulum. Given that \(\alpha = \frac { \pi } { 20 }\) and that \(P Q\) has length \(\frac { 8 } { 33 } \mathrm {~m}\),
  4. find, to 3 significant figures, an approximate value for the angular speed of the pendulum 0.2 s after it has been released from rest.
Edexcel M5 2012 June Q1
9 marks Standard +0.3
  1. A particle \(P\) moves in a plane such that its position vector \(\mathbf { r }\) metres at time \(t\) seconds \(( t > 0 )\) satisfies the differential equation
$$\frac { \mathrm { d } \mathbf { r } } { \mathrm {~d} t } - \frac { 2 } { t } \mathbf { r } = 4 \mathbf { i }$$ When \(t = 1\), the particle is at the point with position vector \(( \mathbf { i } + \mathbf { j } ) \mathrm { m }\).
Find \(\mathbf { r }\) in terms of \(t\).
Edexcel M5 2012 June Q2
10 marks Challenging +1.2
2. A rocket, with initial mass 1500 kg , including 600 kg of fuel, is launched vertically upwards from rest. The rocket burns fuel at a rate of \(15 \mathrm {~kg} \mathrm {~s} ^ { - 1 }\) and the burnt fuel is ejected vertically downwards with a speed of \(1000 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) relative to the rocket. At time \(t\) seconds after launch \(( t \leqslant 40 )\) the rocket has mass \(m \mathrm {~kg}\) and velocity \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\).
  1. Show that $$\frac { \mathrm { d } v } { \mathrm {~d} t } + \frac { 1000 } { m } \frac { \mathrm {~d} m } { \mathrm {~d} t } = - 9.8$$
  2. Find \(v\) at time \(t , 0 \leqslant t \leqslant 40\)
Edexcel M5 2012 June Q3
12 marks Challenging +1.8
  1. A uniform rod \(P Q\), of mass \(m\) and length \(3 a\), is free to rotate about a fixed smooth horizontal axis \(L\), which passes through the end \(P\) of the rod and is perpendicular to the rod. The rod hangs at rest in equilibrium with \(Q\) vertically below \(P\). One end of a light inextensible string of length \(2 a\) is attached to the rod at \(P\) and the other end is attached to a particle of mass \(3 m\). The particle is held with the string taut, and horizontal and perpendicular to \(L\), and is then released. After colliding, the particle sticks to the rod forming a body \(B\).
    1. Show that the moment of inertia of \(B\) about \(L\) is \(15 m a ^ { 2 }\).
    2. Show that \(B\) first comes to instantaneous rest after it has turned through an angle \(\arccos \left( \frac { 9 } { 25 } \right)\).
Edexcel M5 2012 June Q4
6 marks
  1. A body consists of a uniform plane circular disc, of radius \(r\) and mass \(2 m\), with a particle of mass \(3 m\) attached to the circumference of the disc at the point \(P\).
    The line \(P Q\) is a diameter of the disc. The body is free to rotate in a vertical plane about a fixed smooth horizontal axis, \(L\), which is perpendicular to the plane of the disc and passes through \(Q\). The body is held with \(Q P\) making an angle \(\beta\) with the downward vertical through \(Q\), where \(\sin \beta = 0.25\), and released from rest. Find the magnitude of the component, perpendicular to \(P Q\), of the force acting on the body at \(Q\) at the instant when it is released.
    [0pt] [You may assume that the moment of inertia of the body about \(L\) is \(15 m r ^ { 2 }\).]
  2. The points \(P\) and \(Q\) have position vectors \(4 \mathbf { i } - 6 \mathbf { j } - 12 \mathbf { k }\) and \(2 \mathbf { i } + 4 \mathbf { j } + 4 \mathbf { k }\) respectively, relative to a fixed origin \(O\).
Three forces, \(\mathbf { F } _ { 1 } , \mathbf { F } _ { 2 }\) and \(\mathbf { F } _ { 3 }\), act along \(\overrightarrow { O P } , \overrightarrow { Q O }\) and \(\overrightarrow { Q P }\) respectively, and have magnitudes \(7 \mathrm {~N} , 3 \mathrm {~N}\) and \(3 \sqrt { } 10 \mathrm {~N}\) respectively.
  1. Express \(\mathbf { F } _ { 1 } , \mathbf { F } _ { 2 }\) and \(\mathbf { F } _ { 3 }\) in vector form.
  2. Show that the resultant of \(\mathbf { F } _ { 1 } , \mathbf { F } _ { 2 }\) and \(\mathbf { F } _ { 3 }\) is \(( 2 \mathbf { i } - 10 \mathbf { j } - 16 \mathbf { k } ) \mathrm { N }\).
  3. Find a vector equation of the line of action of this resultant, giving your answer in the form \(\mathbf { r } = \mathbf { a } + \lambda \mathbf { b }\), where \(\mathbf { a }\) and \(\mathbf { b }\) are constant vectors and \(\lambda\) is a parameter.
Edexcel M5 2012 June Q6
12 marks Standard +0.8
6. A uniform circular pulley, of mass \(4 m\) and radius \(r\), is free to rotate about a fixed smooth horizontal axis which passes through the centre of the pulley and is perpendicular to the plane of the pulley. A light inextensible string passes over the pulley and has a particle of mass \(2 m\) attached to one end and a particle of mass \(3 m\) attached to the other end. The particles hang with the string vertical and taut on each side of the pulley. The rim of the pulley is sufficiently rough to prevent the string slipping. The system is released from rest.
  1. Find the angular acceleration of the pulley. When the angular speed of the pulley is \(\Omega\), the string breaks and a constant braking couple of magnitude \(G\) is applied to the pulley which brings it to rest.
  2. Find an expression for the angle turned through by the pulley from the instant when the string breaks to the instant when the pulley first comes to rest.
Edexcel M5 2012 June Q7
16 marks Challenging +1.8
  1. (a) A uniform lamina of mass \(m\) is in the shape of a triangle \(A B C\). The perpendicular distance of \(C\) from the line \(A B\) is \(h\). Prove, using integration, that the moment of inertia of the lamina about \(A B\) is \(\frac { 1 } { 6 } m h ^ { 2 }\).
    (b) Deduce the radius of gyration of a uniform square lamina of side \(2 a\), about a diagonal.
The points \(X\) and \(Y\) are the mid-points of the sides \(R Q\) and \(R S\) respectively of a square \(P Q R S\) of side \(2 a\). A uniform lamina of mass \(M\) is in the shape of \(P Q X Y S\).
(c) Show that the moment of inertia of this lamina about \(X Y\) is \(\frac { 79 } { 84 } M a ^ { 2 }\).
Edexcel M5 2013 June Q1
7 marks Moderate -0.3
  1. A particle moves in a plane in such a way that its position vector \(\mathbf { r }\) metres at time \(t\) seconds satisfies the differential equation
$$\frac { \mathrm { d } ^ { 2 } \mathbf { r } } { \mathrm {~d} t ^ { 2 } } - 2 \frac { \mathrm {~d} \mathbf { r } } { \mathrm {~d} t } = \mathbf { 0 }$$ When \(t = 0\), the particle is at the origin and is moving with velocity \(( 4 \mathbf { i } + 2 \mathbf { j } ) \mathrm { m } \mathrm { s } ^ { - 1 }\).
Find \(\mathbf { r }\) in terms of \(t\).
Edexcel M5 2013 June Q2
11 marks Challenging +1.2
2. Three forces \(\mathbf { F } _ { 1 } = ( 3 \mathbf { i } - \mathbf { j } + \mathbf { k } ) \mathrm { N } , \mathbf { F } _ { 2 } = ( 2 \mathbf { i } - \mathbf { k } ) \mathrm { N }\), and \(\mathbf { F } _ { 3 }\) act on a rigid body. The force \(\mathbf { F } _ { 1 }\) acts through the point with position vector \(( \mathbf { i } + 2 \mathbf { j } + \mathbf { k } ) \mathrm { m }\), the force \(\mathbf { F } _ { 2 }\) acts through the point with position vector \(( \mathbf { i } - 2 \mathbf { j } ) \mathrm { m }\) and the force \(\mathbf { F } _ { 3 }\) acts through the point with position vector \(( \mathbf { i } + \mathbf { j } + \mathbf { k } ) \mathrm { m }\). Given that the system \(\mathbf { F } _ { 1 } , \mathbf { F } _ { 2 }\) and \(\mathbf { F } _ { 3 }\) reduces to a couple \(\mathbf { G }\),
  1. find \(\mathbf { G }\). The line of action of \(\mathbf { F } _ { 3 }\) is changed so that the system \(\mathbf { F } _ { 1 } , \mathbf { F } _ { 2 }\) and \(\mathbf { F } _ { 3 }\) now reduces to a couple \(( 6 \mathbf { i } + 8 \mathbf { j } + 2 \mathbf { k } ) \mathrm { N }\) m.
  2. Find an equation of the new line of action of \(\mathbf { F } _ { 3 }\), giving your answer in the form \(\mathbf { r } = \mathbf { a } + t \mathbf { b }\), where \(\mathbf { a }\) and \(\mathbf { b }\) are constant vectors.
Edexcel M5 2013 June Q3
14 marks Challenging +1.2
  1. A spacecraft is moving in a straight line in deep space. The spacecraft moves by ejecting burnt fuel backwards at a constant speed of \(2000 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) relative to the spacecraft. The burnt fuel is ejected at a constant rate of \(c \mathrm {~kg} \mathrm {~s} ^ { - 1 }\). At time \(t\) seconds the total mass of the spacecraft, including fuel, is \(m \mathrm {~kg}\) and the speed of the spacecraft is \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\).
    1. Show that, while the spacecraft is ejecting burnt fuel,
    $$m \frac { \mathrm {~d} v } { \mathrm {~d} t } = 2000 c$$ At time \(t = 0\), the mass of the spacecraft is \(M _ { 0 } \mathrm {~kg}\) and the speed of the spacecraft is \(2000 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). When \(t = 50\), the spacecraft is still ejecting burnt fuel and its speed is \(6000 \mathrm {~m} \mathrm {~s} ^ { - 1 }\).
  2. Find \(c\) in terms of \(M _ { 0 }\).
Edexcel M5 2013 June Q4
13 marks Hard +2.3
4. Show, using integration, that the moment of inertia of a uniform solid right circular cone of mass \(M\), height \(h\) and base radius \(a\), about an axis through the vertex, parallel to the base, is $$\frac { 3 M } { 20 } \left( a ^ { 2 } + 4 h ^ { 2 } \right)$$ [You may assume without proof that the moment of inertia of a uniform circular disc, of radius \(r\) and mass \(m\), about a diameter is \(\frac { 1 } { 4 } m r ^ { 2 }\).]
Edexcel M5 2013 June Q5
15 marks Challenging +1.8
5. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{d3e55cec-05f7-4db3-8eb5-5d0adca38d4c-09_723_707_214_621} \captionsetup{labelformat=empty} \caption{Figure 1}
\end{figure} A uniform circular lamina has radius \(2 a\) and centre \(C\). The points \(P , Q , R\) and \(S\) on the lamina are the vertices of a square with centre \(C\) and \(C P = a\). Four circular discs, each of radius \(\frac { a } { 2 }\), with centres \(P , Q , R\) and \(S\), are removed from the lamina. The remaining lamina forms a template \(T\), as shown in Figure 1. The radius of gyration of \(T\) about an axis through \(C\), perpendicular to \(T\), is \(k\).
  1. Show that \(k ^ { 2 } = \frac { 55 a ^ { 2 } } { 24 }\) The template \(T\) is free to rotate in a vertical plane about a fixed smooth horizontal axis which is perpendicular to \(T\) and passes through a point on its outer rim.
  2. Write down an equation of rotational motion for \(T\) and deduce that the period of small oscillations of \(T\) about its stable equilibrium position is $$2 \pi \sqrt { } \left( \frac { 151 a } { 48 g } \right)$$
Edexcel M5 2013 June Q6
15 marks Challenging +1.2
6. A uniform circular disc, of radius \(r\) and mass \(m\), is free to rotate in a vertical plane about a fixed smooth horizontal axis \(L\) which is perpendicular to the plane of the disc and passes through a point which is \(\frac { 1 } { 4 } r\) from the centre of the disc. The disc is held at rest with its centre vertically above the axis. The disc is then slightly disturbed from its rest position. You may assume without proof that the moment of inertia of the disc about \(L\) is \(\frac { 9 m r ^ { 2 } } { 16 }\).
  1. Show that the angular speed of the disc when it has turned through \(\frac { \pi } { 2 }\) is \(\sqrt { } \left( \frac { 8 g } { 9 r } \right)\).
  2. Find the magnitude of the force exerted on the disc by the axis when the disc has turned through \(\frac { \pi } { 2 }\).
Edexcel M5 2013 June Q1
7 marks Standard +0.8
  1. Solve the differential equation
$$\frac { \mathrm { d } \mathbf { r } } { \mathrm {~d} t } - 2 \mathbf { r } = \mathbf { 0 }$$ given that when \(t = 0 , \mathbf { r } . \mathbf { j } = 0\) and \(\mathbf { r } \times \mathbf { j } = \mathbf { i } + \mathbf { k }\).
Edexcel M5 2013 June Q2
9 marks Challenging +1.2
2. A uniform square lamina \(S\) has side \(2 a\). The radius of gyration of \(S\) about an axis through a vertex, perpendicular to \(S\), is \(k\).
  1. Show that \(k ^ { 2 } = \frac { 8 a ^ { 2 } } { 3 }\). The lamina \(S\) is free to rotate in a vertical plane about a fixed smooth horizontal axis which is perpendicular to \(S\) and passes through a vertex.
  2. By writing down an equation of rotational motion for \(S\), find the period of small oscillations of \(S\) about its position of stable equilibrium.
Edexcel M5 2013 June Q3
7 marks Challenging +1.8
3. A raindrop falls vertically under gravity through a stationary cloud. At time \(t = 0\), the raindrop is at rest and has mass \(m _ { 0 }\). As the raindrop falls, water condenses onto it from the cloud so that the mass of the raindrop increases at a constant rate \(c\). At time \(t\), the mass of the raindrop is \(m\) and the speed of the raindrop is \(v\). The resistance to the motion of the raindrop has magnitude \(m k v\), where \(k\) is a constant. Show that $$\frac { \mathrm { d } v } { \mathrm {~d} t } + v \left( k + \frac { c } { m _ { 0 } + c t } \right) = g$$
Edexcel M5 2013 June Q4
15 marks Challenging +1.2
  1. Three forces \(\mathbf { F } _ { 1 } , \mathbf { F } _ { 2 }\) and \(\mathbf { F } _ { 3 }\) act on a rigid body. The forces \(\mathbf { F } _ { 1 }\) and \(\mathbf { F } _ { 2 }\) act through the points with position vectors \(\mathbf { r } _ { 1 }\) and \(\mathbf { r } _ { 2 }\) respectively. \(\mathbf { r } _ { 1 } = ( - 2 \mathbf { i } + 3 \mathbf { j } ) \mathrm { m }\), \(\mathbf { F } _ { 1 } = ( 3 \mathbf { i } - 2 \mathbf { j } + \mathbf { k } ) \mathrm { N }\) \(\mathbf { r } _ { 2 } = ( 3 \mathbf { i } + 2 \mathbf { k } ) \mathrm { m }\), \(\mathbf { F } _ { 2 } = ( - 2 \mathbf { i } + \mathbf { j } - \mathbf { k } ) \mathrm { N }\) Given that the system \(\mathbf { F } _ { 1 } , \mathbf { F } _ { 2 }\) and \(\mathbf { F } _ { 3 }\) is in equilibrium,
    1. find \(\mathbf { F } _ { 3 }\),
    2. find a vector equation of the line of action of \(\mathbf { F } _ { 3 }\), giving your answer in the form \(\mathbf { r } = \mathbf { a } + t \mathbf { b }\).
    The force \(\mathbf { F } _ { 3 }\) is replaced by a force \(\mathbf { F } _ { 4 }\) acting through the point with position vector \(( \mathbf { i } - 2 \mathbf { j } + 3 \mathbf { k } ) \mathrm { m }\). The system \(\mathbf { F } _ { 1 } , \mathbf { F } _ { 2 }\) and \(\mathbf { F } _ { 4 }\) is equivalent to a single force ( \(3 \mathbf { i } + \mathbf { j } + \mathbf { k }\) ) N acting through the point with position vector \(( \mathbf { i } + \mathbf { j } + \mathbf { k } ) \mathrm { m }\) together with a couple.
  2. Find the magnitude of this couple.
Edexcel M5 2013 June Q5
10 marks Challenging +1.2
5. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{90c52724-f7db-481f-acef-95a24f75b16a-07_561_545_205_705} \captionsetup{labelformat=empty} \caption{Figure 1}
\end{figure} A uniform triangular lamina \(A B C\), of mass \(M\), has \(A B = A C\) and \(B C = 2 a\). The mid-point of \(B C\) is \(D\) and \(A D = h\), as shown in Figure 1. Show, using integration, that the moment of inertia of the lamina about an axis through \(A\), perpendicular to the plane of the lamina, is $$\frac { M } { 6 } \left( a ^ { 2 } + 3 h ^ { 2 } \right)$$ [You may assume without proof that the moment of inertia of a uniform rod, of length \(2 l\) and mass \(m\), about an axis through its midpoint and perpendicular to the rod, is \(\frac { 1 } { 3 } m l ^ { 2 }\).]