The Speed Camera Scandal
The Speed Camera Scandal
A speed camera on the motorway flashes at a car traveling at what appears to be exactly 70 mph. But when the case goes to court, the driver's lawyer argues that the camera measured the car traveling 50 metres in just 2.5 seconds - which actually works out to 44.7 mph, well under the limit! Meanwhile, engineers designing a new bridge need to calculate if the steel beams can handle the pressure from the water below, and a space mission depends on calculating fuel density to ensure the rocket has enough power to escape Earth's gravity. From speed cameras to space rockets, compound measures combine two or more basic measurements to tell us crucial information about our world.
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Exam Success Strategies
- Check your units: Always write the correct units with your answer
- Convert first: Get all measurements in the same units before calculating
- Use formula triangles: Draw them if you get stuck - cover what you want to find
- Average speed ≠ average of speeds: Always use total distance ÷ total time
- Show clear working: Even for simple calculations, show your method
- Reasonableness check: Does your answer make sense? A car speed of 200 m/s is clearly wrong!
Now try it yourself
Quiz · Question 1 of 12
Which formula correctly gives speed in terms of distance and time?
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This topic in real past papers
Every real exam question we've found on compound measures, with a full worked answer.
AQA Paper 2
Three of the four sittings we have full papers for give a real-world rate word problem, needing a rate to be found, then used or converted.
AQA Paper 3
Three of the four sittings we have full papers for give a compound measure formula and ask for it to be applied, often together with its correct units.
Edexcel Paper 2
Two of the three sittings we have full papers for ask for a formula to be rearranged, and June 2019 goes further, requiring the subject to be collected together after it appears on both sides.