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Close your eyes and imagine you are a… …. You start from the bus driver’s home to pick up 5 students from Ang Mo Kio before reaching the school. How do you think the speed which you are traveling will be like? Will it be a constant speed ?. School bus. - PowerPoint PPT Presentation
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Close your eyes and imagine you are a… …
• You start from the bus driver’s home to pick up 5 students from Ang Mo Kio before reaching the school.
• How do you think the speed which you are traveling will be like?
• Will it be a constant speed ?
Constant speed means uniform speed, or steady speed, or fixed speed.
The speed does not change throughout the journey.
Since the bus does not travel in a constant speed, how can we still find out how fast it travels?
Yes!
We use Average Speed.
It is calculated based on the TOTAL distance travelled and the TOTAL time taken.
We know speed is the distance travelled per unit time, hence
Average Speed =Total Distance
Total Time
A cyclist cycled from Serangoon Road to Rosyth School. The cyclist started traveling at 6 a.m. and reached Rosyth School at 7 a.m.
What is the cyclist’s average speed if the distance between Serangoon Road and Rosyth School is 7 km?
Time Taken = 1 h
Average Speed = Total Distance ÷ Total Time = 7 ÷ 1 = 7
The cyclist’s average speed is 7 km/h.
Example
S
D
T Distance = Speed x Time
How to memorise the formula?
Speed =Distance
Time
Time =Distance
Speed
Using this Model, solve the following questions.
John started cycling at 7.30 a.m. By 9.30 a.m. he had covered a distance of 20 km.
Find his average speed in km/h.
S
D
T
Speed =Distance
Time
20 2
=
= 10
John’s average speed is 10 km/h.
Mr Li took 4 hours to drive from Town P to Town Q at an average speed of 75 km/h.
On his way back, he drove at an average speed of 60 km/h.
How long did he take to drive back from Town Q to Town P?Distance between Town P and Q = Speed x Time
= (75 x 4) km = 300 km
Time taken =Distance
Speed
= h300
60
= 5 h
Mr Li took 5 h to drive back.
A motorcyclist took 7 hours to travel from Town X to Town Y at an average speed of 35 km/h.
A van took only 5 hours for the same journey. Find the average speed of the van.
Distance between Town X and Y = Speed x Time = (35 x 7) km = 245 km
Speed =Distance
Time
= km/h245
5
= 49 km/h
The motorist’s speed was 49 km/h.
It’s your turn to solve problems using the formula
S
D
T Distance = Speed x Time
Speed =Distance
Time
Time =Distance
Speed
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