SPEED, DISTANCE AND TIME

Changing units of time 1 Write 24 minutes as a fraction of an hour. to change minutes into hours divide by 60 2 Write 54 minutes as a decimal of an hour. 54 minutes = to change minutes into hours divide by 60 to change a fraction to a decimal divide the numerator by the denominator

3 Change of an hour into minutes. to change hours into minutes multiply by 60 4 Change 0.3 hours into minutes. to change hours into minutes multiply by 60

Speed Speed is a measure of how fast an object is travelling. When the speed is constant, the formula connecting speed, distance and time is: If the distance is measured in metres and the time is measured in seconds then the speed is measured in metres per second (m/s or ms−1). If the distance is measured in kilometres and the time is measured in hours then the speed is measured in kilometres per hour (km/h or kmh−1).

1 A car takes 3 hours 20 minutes to travel 300 km at constant speed. Find the speed of the car in km/h. You must first change 20 minutes into hours.

2 A car is travelling at 54 km/h. Change the speed of the car into m/s. 54 kilometres/hour = 54 000 metres/hour

D S × T The formula can be rearranged to give distance = speed × time The following triangle is a useful memory aid for remembering the three formulae. To find the formula for finding T put your finger over the letter T. D S × T This gives you To find the formula for finding D put your finger over the letter D. This gives you

A bird flies for 48 km at a speed of 6 m/s. Calculate the time taken in hours and minutes. change 48 km into m 48 km = 48 000 m divide by 60 to change into minutes 120 minutes = 2 hours

Average speed You can calculate the average speed for a journey using:

A car travels at 75 km/h for 3 hours and then at 60 km/h for 30 minutes. a Calculate the total distance travelled. b Calculate the average speed for the whole journey. a distance = speed × time Total distance = 225 + 30 = 255 km b