You can calculate average speed using this equation:
Calculate the average speed of a runner who runs 100 m in 10 s.
average speed = 100 ÷ 10 = 10 m/s
Notice that the unit for speed in science is metres per second, m/s. It is not, for example, mph, kph or m per s.
If you are given the distance travelled in km, multiply it by 1000 to get the distance in m. For example, 3.5 km is 3500 m (3.5 × 1000).
A car travels 2 km in 100 s. Calculate its average speed.
2 km = 2 × 1000 = 2000 m
average speed = 2000 ÷ 100 = 20 m/s
Speed cameras are used to find out if a motorist is travelling faster than the speed limit for the road. The camera takes two photographs of the vehicle. These can be:
The speed limit on a road is 13.4 m/s (30 mph). Calculate the distance travelled by a car in 2 s at this speed.
average speed = distance ÷ time
Rearranging this equation:
distance = average speed × time
= 13.4 × 2 = 26.8 m
Calculate the time taken for the car to travel 50 m at this speed.
Rearranging the equation:
time = distance ÷ average speed
= 50 ÷ 13.4 = 3.7 s