Edexcel M2 (Mechanics 2) 2021 January

1. A particle \(P\) of mass 1.5 kg is moving with velocity \(( 4 \mathbf { i } + 6 \mathbf { j } ) \mathrm { m } \mathrm { s } ^ { - 1 }\) when it receives an impulse of magnitude 15Ns. Immediately after \(P\) receives the impulse, the velocity of \(P\) is \(\boldsymbol { v } \mathrm { m } \mathrm { s } ^ { - 1 }\).

Find the two possible values of \(v\).

2. \begin{figure}[h] \end{figure} The uniform lamina \(A B C\) has sides \(A B = A C = 13 a\) and \(B C = 10 a\). The lamina is freely suspended from \(A\). A horizontal force of magnitude \(F\) is applied to the lamina at \(B\), as shown in Figure 1. The line of action of the force lies in the vertical plane containing the lamina. The lamina is in equilibrium with \(A B\) vertical. The weight of the lamina is \(W\). Find \(F\) in terms of \(W\).
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3. A car of mass 600 kg travels along a straight horizontal road with the engine of the car working at a constant rate of \(P\) watts. The resistance to the motion of the car is modelled as a constant force of magnitude \(R\) newtons. At the instant when the speed of the car is \(15 \mathrm {~ms} ^ { - 1 }\), the magnitude of the acceleration of the car is \(0.2 \mathrm {~ms} ^ { - 2 }\). Later the same car travels up a straight road inclined at angle \(\theta\) to the horizontal, where \(\sin \theta = \frac { 1 } { 20 }\). The resistance to the motion of the car from non-gravitational forces is modelled as a constant force of magnitude \(R\) newtons. When the engine of the car is working at a constant rate of \(P\) watts, the car has a constant speed of \(10 \mathrm {~ms} ^ { - 1 }\). Find the value of \(P\).

4. \begin{figure}[h] \end{figure} The number "4", shown in Figure 2, is a rigid framework made from three uniform rods, \(A B , B C\) and \(C D\), where $$A B = 6 a , B C = 5 a \text { and } C D = 4 a$$ The point \(E\) is on \(A B\) and \(C D\), where \(B E = 4 a , C E = 3 a\) and angle \(C E B = 90 ^ { \circ }\) The three rods are all made from the same material and they all lie in the same plane. The framework is suspended from \(B\) and hangs in equilibrium with \(B A\) at an angle \(\theta\) to the downward vertical. Find \(\theta\) to the nearest degree.
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5. At time \(t\) seconds, \(t \geqslant 0\), a particle \(P\) has velocity \(\mathbf { v } \mathrm { ms } ^ { - 1 }\), where $$\mathbf { v } = \left( 5 t ^ { 2 } - 12 t + 15 \right) \mathbf { i } + \left( t ^ { 2 } + 8 t - 10 \right) \mathbf { j }$$ When \(t = 0 , P\) is at the origin \(O\).
At time \(T\) seconds, \(P\) is moving in the direction of \(( \mathbf { i } + \mathbf { j } )\).

1. Find the value of \(T\). When \(t = 3 , P\) is at the point \(A\).
2. Find the magnitude of the acceleration of \(P\) as it passes through \(A\).
3. Find the position vector of \(A\).

6. \begin{figure}[h] \end{figure} A ladder \(A B\) has length 6 m and mass 30 kg . The ladder rests in equilibrium at \(60 ^ { \circ }\) to the horizontal with the end \(A\) on rough horizontal ground and the end \(B\) against a smooth vertical wall, as shown in Figure 3. A man of mass 70 kg stands on the ladder at the point \(C\), where \(A C = 2 \mathrm {~m}\), and the ladder remains in equilibrium. The ladder is modelled as a uniform rod in a vertical plane perpendicular to the wall. The man is modelled as a particle.

1. Find the magnitude of the force exerted on the ladder by the ground. The man climbs further up the ladder. When he is at the point \(D\) on the ladder, the ladder is about to slip. Given that the coefficient of friction between the ladder and the ground is 0.4
2. find the distance \(A D\).
3. State how you have used the modelling assumption that the ladder is a rod.

7. \begin{figure}[h] \end{figure} The fixed point \(A\) is 20 m vertically above the point \(O\) which is on horizontal ground. At time \(t = 0\), a particle \(P\) is projected from \(A\) with speed \(12 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) at an angle \(\theta ^ { \circ }\) above the horizontal. The particle moves freely under gravity. At time \(t = 5\) seconds, \(P\) strikes the ground at the point \(B\), where \(O B = 40 \mathrm {~m}\), as shown in Figure 4.

1. By considering energy, find the speed of \(P\) as it hits the ground at \(B\).
2. Find the least speed of \(P\) as it moves from \(A\) to \(B\).
3. Find the length of time for which the speed of \(P\) is more than \(10 \mathrm {~ms} ^ { - 1 }\).

8. Two particles, \(A\) and \(B\), have masses \(3 m\) and \(4 m\) respectively. The particles are moving towards each other along the same straight line on a smooth horizontal surface. The particles collide directly. Immediately after the collision, \(A\) and \(B\) are moving in the same direction with speeds \(\frac { u } { 3 }\) and \(u\) respectively. In the collision, \(A\) receives an impulse of magnitude 8mu.

1. Find the coefficient of restitution between \(A\) and \(B\). When \(A\) and \(B\) collide they are at a distance \(d\) from a smooth vertical wall, which is perpendicular to their direction of motion. After the collision with \(A\), particle \(B\) collides directly with the wall and rebounds so that there is a second collision between \(A\) and \(B\). This second collision takes place at distance \(x\) from the wall. Given that the coefficient of restitution between \(B\) and the wall is \(\frac { 1 } { 4 }\)
2. find \(x\) in terms of \(d\).
   

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