Calculate cost of 5 mm x 5 mm cross section square bar with a length of 4 meters made of metal with density 3 grams/cubic centimetre. Unit cost of metal is Rs. 1000/kg.  

Concept:

Density = \(\frac{Mass}{Volume}\)

Volume of the cubical bar = length × width × height

Calculation:

Given:

cross-section of the square bar = 5 mm x 5 mm = 0.005 m × 0.005 m

Length of the bar = 4 m, Unit cost of metal is Rs1000/kg.  

Density of metal = 3 grams/cubic centimeter = \(\frac{3}{1000}~×~\frac{1}{10^{-6}}~Kg/m^3\)

⇒ Density of metal = 3000 Kg/m³

∵ Volume of the cubical bar = 0.005 m × 0.005 m × 4 = 0.0001

Density = \(\frac{Mass}{Volume}\)

⇒ 3000 = \(\frac{Mass}{0.0001}\)

⇒ Mass = 0.3 Kg

Cost of the square bar = 0.3 × 1000 = Rs 300