a cubic metre of copper weighing 9002 kg is rolled into a square bar 9 metres. An exact cube is cut off from the bar how much does it weigth

Let the width of the square cross section be w.  Then 9*w^2 = 1 so w = sqrt(1/9) = 1/3 m

 

The volume of a cube of width w is therefore w^3 or 1/27 m^3

 

This weighs 9002/27 kg.