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Speed, distance and time
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How fast is a sprinter? How far does a car go in a minute? One equation answers both.
The equation
distance = average speed × time, or s = v × t
Rearranged: speed = distance ÷ time, and time = distance ÷ speed.
Use metres and seconds to get m/s.
Rearranged: speed = distance ÷ time, and time = distance ÷ speed.
Use metres and seconds to get m/s.
Velocity
Velocity is speed in a given direction. A car going round a roundabout at a steady speed has a changing velocity, because its direction changes.
Distance-time graphs
The gradient (steepness) of a distance-time graph is the speed.
A flat line means the object is stationary. A steeper line means faster.
A flat line means the object is stationary. A steeper line means faster.
A cyclist travels 3 km in 10 minutes. Find the average speed in m/s.
- Convert: 3 km = 3000 m and 10 minutes = 600 s.
- speed = distance ÷ time = 3000 ÷ 600
- = 5 m/s
Answer: 5 m/s
speed = distance ÷ time in m and s. Velocity is speed with a direction. On a distance-time graph, the gradient is the speed.
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