STARTER
A runner runs 30m in 5 seconds. How far do
they travel in 1 second?
A hurdler covers 110m in 12.2 seconds. How far
do they travel in 1 second? (to 2 decimal places)
30 ÷ 5
110 ÷ 12.2
= 6 metres per second
= 9.016393443
= 9.02 metres per second
A train travels 1,000m in 25 seconds. How
far does it travel in 1 second?
A plane travels 150,000m in 1800 seconds. How
far does it travel in 1 second?
1000 ÷ 25
150,000 ÷ 1800
= 40 metres per second
= 83.333333333
= 83.33 metres per second
CHAPTER 20
TIME AND RATES OF CHANGE
20.1 AVERAGE SPEED
20.2 COMPOUND MEASURES
Learning objectives:
• solve problems involving average speed,
• use compound measures to make comparisons in
Success criteria:
• calculate the average speed and solve problems
involving average speed accurately.
UNITS OF TIME
• 60 seconds = 1 minute
• 60 minutes = 1 hour
• 24 hours = 1 day
• 1 week = 7days
• 2 weeks = fortnight
• 28-31 days = 1 month
• 12 months = 1 year
• 365/366 days = 1 year
AVERAGE SPEED
Units of speed:
𝒌𝒎
= 𝒌𝒎/𝒉
𝒉
𝒎
= 𝒎/𝒔
𝒔
𝒎𝒊𝒍𝒆𝒔
= 𝒎𝒑𝒉
𝒉
A truck goes from Haryana to Bangalore with an average speed
of 60 km/hr. The journey takes 30 hours. It returns from
Bangalore to Haryana on the same road with an average speed
of 40 km/hr. What was the average speed of the truck during the
roundtrip?
A) 50 km/hr
52 km/hr
B) 55 km/hr
C
C) 48 km/hr
D)
COMPOUND MEASURES
Name examples of compound measures
Density
The density of a rock is 2.75g/cm3. Using the unit, can you guess the
formula for density?
𝑚𝑎𝑠𝑠
𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =
?
𝑣𝑜𝑙𝑢𝑚𝑒
This is a rock.
If the volume of a rock is 0.06m3,
what is its mass?
Population Density
The population density of a Slovenia is 103.51people/km2.
Using the unit, can you guess the formula for population density?
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑒𝑜𝑝𝑙𝑒
?
𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =
𝑎𝑟𝑒𝑎
If the population of Slovenia is 2112000, how big is its area?
Classwork:
Strategies if you get stuck:
Canvas:
Compound measures Codebreaker
*Challenge:
EX 20.1:
10, 12, 14, 15, 16
EX 20.2:
4, 5
• research (notebook, textbook, internet)
• ask your classmates or the teacher
Additional work:
EX 20.1:
1-9
EX 20.2:
1-3