4.
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\caption{Figure 2}
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A non-uniform rod \(A B\) has length 6.5 m and mass 1.2 kg . The centre of mass of the rod is 3 m from \(A\). The rod rests on a horizontal step and overhangs the end of the step \(C\) by 1.5 m , as shown in Figure 2.
The rod is perpendicular to the edge of the step.
A particle of mass 4 kg is placed on the rod at \(B\) and another particle, whose mass is \(M \mathrm {~kg}\), is placed on the rod at \(D\), where \(A D = 0.5 \mathrm {~m}\).
The rod remains in equilibrium in a horizontal position.
- Find the smallest possible value of \(M\).
The particle at \(B\) and the particle at \(D\) are now removed.
A new particle is placed on the rod at the point \(E\), where \(E B = 0.9 \mathrm {~m}\).
The rod remains in equilibrium in a horizontal position but is on the point of tilting about \(C\). - Find the magnitude of the force acting on the rod at \(C\).