Speed Distance and Time

What is to be learned

• How to calculate average speed, given the time taken and distance travelled in a journey

• Correct units for speed

• How to cope with converting hours and minutes into decimals

Calculating Speed

A car travels at 50 mph

Would travel 50 miles in one hour going at same speed

Speed of car that travels 120 miles in 3 hours?

Speed = 120 ÷ 3

= 40 mph

Average Speed = Distance ÷ Time

Calculating Speed

Average Speed = Distance ÷ Time

Written as S = D/T

Percy drives 240 km in 4 hours

S = D/T

= 240/4

= 60 km per hour

Units

Always dist unit per time unit

miles per hour

metres per second

cm per day

mm per month!

Danger

Beware time difficulties

2 hours 30 mins = 2.30

2 ½ hours = 2.5

There are not 100 minutes in an hour!

Time difficulties!

Remember ½ = 0.5¼ = 0.25¾ = 0.75

S0 5 hours 15 mins= 5 ¼ hours= 5.25 hours (for calculator)4 hours 45 mins= 4 ¾ hours = 4.75 hours

Barney’s bus takes 2 ½ hours

to travel 75 miles.

What is his average speed?

S = D/T

= 75/2.5

= 30 mph

Calculating Speed

Average Speed = Distance ÷ Time

S = D/T

Beware time difficulties!Remember

½ = 0.5¼ = 0.25¾ = 0.75

S0 3 hours 15 mins= 3 ¼ hours= 3.25 hours (for calculator)

Train leaves Glasgow at 6:10 and arrives at Oban at 7:55. The journey is 95 miles.

Average speed?

S = D/T Time?1hour 45 mins= 1 ¾ hours= 1.75 hours

so S = 95/1.75

= 54.3 mph