Speed

Speed is a measure of how fast something is travelling.

It is the distance travelled in 1 second (or in 1 hour).

Triangle showing how speed, distance or time can be calculated.d = distance (m); s = speed (m/s); t = time (s)

Speed is measured in m/s or km/h (or mph in UK cars).

\text{speed}=\frac{\text{distance travelled}}{\text{time taken}}

Speed, or distance, or time can be calculated using the dst triangle.

Cover the letter you want to find to get the formula you need.

  • d = s × t
  • s = d ÷ t
  • t = d ÷ s
Question

If a car travels 24 m in 2 seconds, what is its speed?

Speed = distance travelled ÷ time

24 m ÷ 2 s = 12 m/s.

The car has a speed of 12 m/s.

If the initial speed and the final speed of an object are known, then the average speed of the object over the journey can be calculated using the equation:

Average speed = \frac{\text{initial speed + final speed}}{\text{2}}

Question

A car travelling at 22 m/s increases its speed to 30m/s. Find its average speed over the journey.

Final speed = 30 m/s

Initial speed = 22 m/s

Average speed = \frac{\text{final speed + initial speed}}{\text{2}}

Average speed = (22 m/s + 30 m/s) ÷ 2 = 52m/s ÷ 2 = 26 m/s.

The average speed of the car is 26 m/s.

There are two equations for average speed:

curriculum-key-fact
Average speed = \frac{\text{total distance}}{\text{total time}}
curriculum-key-fact
Average speed = \frac{\text{initial speed + final speed}}{\text{2}}

You decide which equation to use, depending on the quantities given in the question.