Speed formula
The formula for the average speed of an object is given below.
It is made up of three parts, distance, time and ofcourse speed. If we know any two of these we can find the third.
For example . If we know the speed of an object and the time over which it travelled we can work out the distance it covered. We first change the formula to make it equal to distance. This easily done by transposition. Look at the image on the right.
Ask your teacher for more information on transposing formulae.
Try this exercise. A car travelled at an average speed of 55km/hr for 6 hours. How far did it travel?
Easy. Using the formula for
distance below
Distance = speed X
time
we calculate
Distance = 55 X 6 = 330 kilometres.
*Note that we must take care with the units.Eg. If the speed is given in km/hr then time must be in hours and distance will be given in kilometres.
Exercises.
a) A car has
an average speed of 34 km/hr for a period of 5 hours. How far did it
travel?
b ) A bullet has an average speed of 45m/sec how far will it travel
in 20 seconds?
c) A train travels at a constant speed of 50km/hr. How far will it travel
in 30 minutes?
Solution
Try this exercise. A car travelled at an average speed of 55km/hr over a distance of 36 km. How long did it take to cover the distance?
Easy. Using the formula for
time below
Distance/speed = time
we calculate
Time = 36 / 55 = 0.6545 hours or 39.27 minutes.
*Note that we must take care with the units.Eg. If the speed is given in km/hr then time must be in hours and distance will be given in kilometres.
Exercises.
a) A car has
an average speed of 34 km/hr. How long will it take to travel 98km?
b ) Jonathon has a car with a maximum speed of 80km/hr. He has to travel
to Melbourne which is 450km away. How long will it take to reach Melbourne
if the car travelled at maximum speed?
c) A train travels at a constant speed of 50km/hr how long will it take
to reach a country town 880km away?
Solution