3 A uniform plank, of length 8 metres, has mass 30 kg . The plank is supported in equilibrium in a horizontal position by two smooth supports at the points \(A\) and \(B\), as shown in the diagram. A block, of mass 20 kg , is placed on the plank at point \(A\).
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1. Draw a diagram to show the forces acting on the plank.
2. Show that the magnitude of the force exerted on the plank by the support at \(B\) is \(19.2 g\) newtons.
3. Find the magnitude of the force exerted on the plank by the support at \(A\).
4. Explain how you have used the fact that the plank is uniform in your solution.