Distance Speed Time

Distance, Speed, Time

Distance = Speed x Time

Time = Distance / Speed

Speed = Distance / Time

Average Speed = Total Distance Travelled / Total Time Taken

Example

Melissa cycles at 10 km/h for 30 minutes and walks 4 km at an average speed of 2 km/h. Find (a) the distance she cycled (b) the time she took for walking (c) average speed for the whole journey.

(a) the distance she cycled

Distance = Speed x Time = 10 km/h x 30 minutes = 10 km/h x (30/60) h = 5 km

(b) the time she took for walking

Time = Distance / Speed = 4 km / 2 km/h = 2 h

(c) average speed for the whole journey

Average Speed = Total Distance Travelled / Total Time Taken

= (5 + 4) km / (1/2 + 2) h

= 9 km / 2.5 h

= 3.6 km/h

Conversion of Speed Units

Speed – Time Graph

Time is in the x axis. Speed is in the y axis.

Distance travelled is the area under the graph.

Acceleration is the gradient.

Questions

1. Express 36 km/h in m/s
2. Express 20 m/s in km/h
3. A bus starts at 0900 travels 100 km at 60 km/h. Find the time when it reaches its destination.
4. Alan's school is 2 km away from his home. He cycles to school at an average speed of 10 km.h. Find how long he will take to reach his school.