RATIO & PROPORTION
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Speed
Speed means “How fast one object is moving.”
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Speed
The rate of change of distance with respect to time
measures in:
Metres per second (m/s)
Kilometres per hour (km/h)
Miles per hour (mph)
𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆
𝒔𝒑𝒆𝒆𝒅 =
𝒕𝒊𝒎𝒆
𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆
𝑻𝒊𝒎𝒆 =
𝒔𝒑𝒆𝒆𝒅
𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆 = 𝒔𝒑𝒆𝒆𝒅 x 𝒕𝒊𝒎𝒆
Speed
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EXAMPLE - 1
Jewel goes to school in her dad’s car every morning. Her school is 8 km from her home,
and she takes 15 mins to travel . Then find the speed of the car in km / h.
Distance , d = 8 km
Time ,t = 15 min
= ¼ h = 0.25 h
𝑑
Speed =
𝑡
=
8
0.25
= 32 km/h
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EXAMPLE - 2
Sarah drove from Sheffield to Peebles in 3.5 hours at an average speed of 60 mph. How
far is it from Sheffield to Peebles?
Distance = Speed x Time
= 60 x 3.5
= 210 miles
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EXAMPLE - 3
Sean is going to drive from Newcastle upon Tyne to Nottingham, 190 miles. He estimates
that he will drive at an average speed of 50 mph. How long will it take him?
Time =
=
Distance
Speed
190
50
= 3.8 hours
= 3h 48mins
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Pressure
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Pressure
Pressure is the force per unit area.
Pressure = force (in N)
area (m2 or cm2)
If the area is in m2, the pressure is in N/m2 (or Pascal: Pa)
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Density
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Density
To calculate the density, we divide the mass of the object by the volume measured in
Grams per cubic centimetre (g/cm³)
Kilograms per cubic metre (kg/m³)
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Example -1
P=
120
2
= 60
60
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Example -2
Volume =
=
𝑚𝑎𝑠𝑠
𝑑𝑒𝑛𝑠𝑖𝑡𝑦
56
3.5
16
=16
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