Question

external dimension of a wooden box are 18 cm ,10 cm,6 cm; thickness of the wood is 5 mm . Empty box weighs 3.15kg. 
 Find the weight of 1 cubic cm wood.

Answer 1

External dimensions are : A = 18cm, B = 10 cm,  C = 6cm
thickness: T = 5mm = 0.5 cm
Each side of the box it is 0.5 cm thick. The hollow portion inside has a length       A'" = A - 2 * thickness , as along a dimension of a box we have two surfaces having thickness 0.5 cm.
The hollow box (empty space inside box) has size : A" = 18 - 2 * 0.5cm = 17cm
  B" = 10 - 2 * 0.5 = 9cm  and C" = 5cm
External volume of box = V = A B C = 1080 cm³
Internal hollow part of box = W = A" B" C" = 17*9*5 cm³
Actual volume of wood in box = V - W = 315 cm³
Weight per 1 cubic cm of wood = 3.15 / 315 = 0.01 kg/cm³

Answer 2

Answer:

External dimensions are : A = 18cm, B = 10 cm,  C = 6cm

thickness: T = 5mm = 0.5 cm

Each side of the box it is 0.5 cm thick. The hollow portion inside has a length       A'" = A - 2 * thickness , as along a dimension of a box we have two surfaces having thickness 0.5 cm.

The hollow box (empty space inside box) has size : A" = 18 - 2 * 0.5cm = 17cm

  B" = 10 - 2 * 0.5 = 9cm  and C" = 5cm

External volume of box = V = A B C = 1080 cm³

Internal hollow part of box = W = A" B" C" = 17*9*5 cm³

Actual volume of wood in box = V - W = 315 cm³

Weight per 1 cubic cm of wood = 3.15 / 315 = 0.01 kg/cm³

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