An edge of a hollow iron cube measures 10 cm. the cube has a uniform wall thickness of 2.5 cm and a square hole at the top. find the mass of the cube in kiligrams if the density of iron is 7.9*10^3 g/cm^3.

To find mass of the cube first find volume of cube material 

edge of cube = 10 cm 
edge of inner cube (hollow space) = 10 - (2.5+2.5) = 5 cm 

total volume of cube = 10^3 = 1000 
total volume empty space = 5^3 = 125 
Volume of cube material = 1000 - 125 = 875 cm^3 

Mass of cube = density x volume = 7.9x10 x 875 = 69125 g = 69.125 kg 

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