Question

H. Numerical problems.
1. 80 cm of iron weighs 624 g. Calculate the
density of iron.
2. A stone piece weighs 225 g. By
displacement method, its volume was found
to be 75 cm". What is the density of the
stone piece?
3. The density of copper is 8.9 g/cmFind its
value in kg/mº
4. A cuboidal object of side 15 cm weighs
1.35 kg. Calculate its density in kg/mº.​

Answer 1

Answer:

1.An 80cm cube has a volume of V = 0.8^3 = 0.512m^3

This is said to “weigh” 624g = 0.624kg (which is a mass, not a weight). But that would produce a density of ρ = m/V = 0.624kg/0.512m^3 = 1.219kg/m^3

And while the calculation is correct, the answer is nonsense, since the density of iron is approximately 7870kg/m^3, and this calculation shows the density as 1.219kg/m^3 – which is close to the density of nitrogen gas!

Following Philip Kloppers suggestion, IF the “80cm cube” meant 80cm^3, which would be 8x10^-5m^3, then the density would be calculated as:

ρ = 0.624kg/8x10^-5m^3 = 7800kg/m^3 which is at least, close to reality.

4.Mass (m) = 1.35 kg

Side (a) = 15 cm = 0.15 m

Volume of a cube = side x side x side = 0.153 = 0.003375 cu. M

Density (ρ) = Mass (m) / Volume (V)

=> ρ = 1.35/0.003375

=> ρ = 400 Kg/m3

Explanation: