Explorers in the jungle find an ancient monument in the shape of a large isoscel

Question

Explorers in the jungle find an ancient monument in the shape of a large isosceles triangle as shown in the figure below. The monument is made from tens of thousands of small stone blocks of density3 191kg/m3. The monument is15.5m high and69.1m wide at its base and is everywhere3.50m thick from front to back. Before the monument was built many years ago, all the stone blocks lay on the ground. How much work did laborers do on the blocks to put them in position while building the entire monument?Note: The gravitational potential energy of an object-Earth system is given byUg=MgyCM, whereMis the total mass of the object andyCMis the elevation of its center of mass above the chosen reference level.
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Explanation / Answer

Total mass of bricks = density*volume = 3191*(1/2*15.5*69.1*3.5) = 5981011 kg

Height of C.G of monument y = 1/3*15.5 = 5.167 m

Work done on the bricks = change in potential energy of the bricks = mgy = 5981011*9.81*5.167 = 3.031*108 J

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