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- Compound measures: speed, density and pressure
Compound measures: speed, density and pressure
Compound measures combine two quantities. Three formula triangles cover almost every question.
The formulae
speed = distancetime
density = massvolume
pressure = forcearea
density = massvolume
pressure = forcearea
Rearranging
distance = speed × time; time = distance ÷ speed
mass = density × volume; volume = mass ÷ density
force = pressure × area
mass = density × volume; volume = mass ÷ density
force = pressure × area
Time units
Watch out for minutes: 1 hour 15 minutes = 1.25 hours, not 1.15.
20 minutes = 2060 = 13 hour.
20 minutes = 2060 = 13 hour.
A car travels 90 km in 1 hour 30 minutes. Find its average speed.
- 1 hour 30 minutes = 1.5 hours
- 90 ÷ 1.5 = 60
Answer: 60 km/h
Speed = distance ÷ time, density = mass ÷ volume, pressure = force ÷ area. Rearrange as needed and convert minutes to hours carefully.
The interactive lesson includes the diagrams for this topic.
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