← Chapter 39 Chapter 40: Compound Units Chapter 41 →

Chapter 40: Compound Units (Speed, Density, Unit Pricing)

✏️ Explanation

Compound units combine two different measurements. Speed = distance ÷ time, density = mass ÷ volume, unit price = cost ÷ quantity.

🔍 Why It Matters

Essential for physics, comparing value for money, and understanding rates in real life.

📌 Visual Flowchart

🧭 See chart: "Compound Units Calculator" (to be added)

✏️ Worked Example

A car travels 150 miles in 3 hours. What's its average speed?
Solution: Use the speed formula
Speed = 150 ÷ 3 = 50 mph

🧮 Compound Units Calculator

Speed = 50 units

🔢 Practice Exercises

1. Find speed: 240km in 4 hours
Speed: km/h
2. Find density: mass 500g, volume 20cm³
Density: g/cm³
3. Which is better value: 500g for £3 or 750g for £4?
4. A train travels at 80km/h for 2.5 hours. Find distance.
Distance: km
5. Density is 2.5g/cm³, volume is 40cm³. Find mass.
Mass: g

⚠️ Common Mistakes

  • Wrong formula (multiplying instead of dividing)
  • Unit confusion (km/h vs m/s)
  • Not converting units consistently

✨ Quick Summary

Compound units = first quantity ÷ second quantity. Watch your units.