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  1. Problems
  2. /A car goes 16 km on one litre of petrol…
EasyChemistryHigh School (11–12)Atoms and Molecules › Measurement, Units and Significant FiguresNumericalBoard Exam

A car goes 16 km on one litre of petrol…

StemPy LabContributed by StemPy Lab

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

A car goes 16 km16\ \text{km}16 km on one litre of petrol. A trip is 240 km240\ \text{km}240 km long, and petrol has a density of 0.74 kg/L0.74\ \text{kg/L}0.74 kg/L. How many litres of petrol does the trip use, and what is their mass?

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Work it out on paper, then type your number. The answer itself stays hidden.

L
kg
Need a reminder? The key ideaShowHide

A conversion factor is a fraction equal to one, such as 1000 mL1 L\dfrac{1000\ \text{mL}}{1\ \text{L}}1 L1000 mL​. Choose it so that the unwanted unit cancels. For squared or cubed units, square or cube the factor.

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.

Step 1. Volume. 240 km×1 L16 km=15 L240\ \text{km} \times \dfrac{1\ \text{L}}{16\ \text{km}} = 15\ \text{L}240 km×16 km1 L​=15 L.

Step 2. Mass. 15 L×0.74 kg1 L=11.1 kg15\ \text{L} \times \dfrac{0.74\ \text{kg}}{1\ \text{L}} = 11.1\ \text{kg}15 L×1 L0.74 kg​=11.1 kg, which is 11 kg11\ \text{kg}11 kg to 2 significant figures.

Answer: 15 L15\ \text{L}15 L, with a mass of about 11 kg11\ \text{kg}11 kg.

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  1. Units and dimensional analysisMatter and Measurement

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