WAEC Physics 2018 Paper

Concept:For a body at equilibrium, the sum of the upward forces equals the sum of the downward forces.Explanation:The bar is stationary, so it is in equilibrium.Each knife edge exerts an upward reaction on the bar.From the diagram, the upward reaction at each knife edge is $20.0\,\mathrm{N}$.Thus, the total upward reaction is $20.0\,\mathrm{N} + 20.0\,\mathrm{N} = 40.0\,\mathrm{N}$.The weight $W$ of the bar is the only downward force.Therefore, $W$ equals the total upward reaction, so $W = 40.0\,\mathrm{N}$.Answer:$W = 40.0\,\mathrm{N}$, so the correct option is C.