Speed
Speed is calculated using the equation:
\(\text{speed}=\frac{\text{distance}}{\text{time}}\)
This is an example of a compound measure because distance and time can’t be measured in the same unit. Speed can be measured in metres per second, kilometres per hour and several other forms too.
Question
Calculate the average speed of a mongoose if it travels 4 km in 0.25 hours.
\(\text{speed}=\frac{\text{distance}}{\text{time}}\)
\(\text{speed}=\frac{\text{4~km}}{\text{0.25~hours}}\)
\(\text{speed = 16 km/h}\)
Question
Calculate the average speed of a cheetah if it travels 300 m in 10 s.
\(\text{speed}=\frac{\text{distance}}{\text{time}}\)
\(\text{speed}=\frac{\text{300~m}}{\text{10~s}}\)
\(\text{speed = 30 m/s}\)
The equation for speed can also be rearranged into either of the following forms:
\(\text{distance}=\text{speed}\times{\text{time}}\)
or
\(\text{time}=\frac{\text{distance}}{\text{speed}}\)
This allows you to calculate either distance or time.
Question
A car travels from Cardiff to London with an average speed of 50 Miles per hour. If the journey takes three hours, estimate the distance from Cardiff to London.
\(\text{distance}=\text{speed}\times{\text{time}}\)
\(\text{distance}=\text{50~mph}\times{\text{3~hours}}\)
\(\text{distance}=\text{150~miles}\)
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