EasyPhysicsHigh School (11–12)Mechanics › Units and MeasurementNumerical

The density of iron is 7.8 g/cm³. Write it in kg/m³.

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

The density of iron is $7.8\ \text{g/cm}^3$ .

Write it in $\text{kg/m}^3$ .
What is the volume of a $2.0\ \text{kg}$ iron dumbbell, in cubic centimetres?

Need a reminder? The key ideaShow

To change a unit, multiply by a fraction that equals one, such as $\dfrac{1000\ \text{m}}{1\ \text{km}}$ , so that the old unit cancels. A prefix goes with the unit's power:

\displaystyle 1\ \text{cm}^2 = (10^{-2}\ \text{m})^2 = 10^{-4}\ \text{m}^2, \qquad 1\ \text{cm}^3 = 10^{-6}\ \text{m}^3

Density is mass over volume, $\rho = m/V$ .

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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