figure 3.1 shows a rectangular concrete slab of weight 18000N. It rests on a brick wall and is the roof of a bus shelter. The concrete slab is 3.0 m wide.
The wall is 2.5 m from the front of the concrete slab and 0.50 m from the back. The cables behind the shelter pull downwards and stop the slab toppling forward.

The concrete slab is of uniform thickness and density. Determine the perpendicular distance between the wall and the centre of mass of the slab?

State the principle of movement?

Calculate the total downward force exerted by the cables on the slab?

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  1. center of mass of slab is in the center, so it is at1.5 m from the front, or from the wall, 1.0m

    now to balance it,
    Fc=force cables are pulling downward
    Fw=force on the wall downward
    sum forces=0
    moments about any point is zero, choose the wall point

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