Chhattisgarh Board Solutions for Chapter: Measurement, Exercise 3: Answer these

What does the statement "Iron is heavier than wood," mean?

What is meant by density? Give its SI units.

The mass of a material contained in $10 {\mathrm{cm}}^3$ is $10000 \mathrm{kg}$. Calculate its density in $\raisebox{1ex}{$\mathrm{kg}$}\!\left/ \!\raisebox{-1ex}{${\mathrm{m}}^3$}\right.$ .

Why is it essential that different parts of a machine fitting into each other have the same measure?

The distance between two stations is $240 \mathrm{km}$. A train covers this distance in $4$ hours. Find the speed of the train in $\raisebox{1ex}{$\mathrm{km}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{h}$}\right.$.