SPEED

Back to: Mathematics Primary 5

HELLO, WELCOME BACK TO CLASS

 

There are many ways of moving from one place to another. You can move by walking, running, riding a bicycle or motorcycle, driving a car or travelling by train or by air. In each type of movement, the time taken at a fixed distance is important. It is important to take note of the time when the journey started and the time the journey ended. In comparing the distance covered with the time spent for the journey, we get the speed taken.

Speed is therefore the rate at which anything is moving or travelling. It is measured by the distance it travels per unit of time. The unit for speed is kilometer per hour (km/hr) or meter per seconds (m/s).

   Average speed = total distance travelled ÷ total time taken

Examples:

1. A train travelled 56km in 2 hours. At what average speed was it travelling?

Solution:

Average speed = total distance travelled ÷ total time taken

= 56km ÷ 2hr = 28km/hr

     Distance is the measure of space between two places

Distance = speed × time

2. Find the distance covered by a car with an average speed of 10km/hr in 4 hours.

Solution:

Distance = speed × time

= 10km/hr × 4 = 40km

Time = Distance ÷ Speed

3. A cyclist has an average speed of 6km/hr, how long would it take to cover a distance of 72km?

Solution :

 Speed = 6km/hr.

Distance = 72km

Time = Distance ÷ Speed

Time = 72 ÷ 6 = 12hrs.

 

PROBLEMS ON AVERAGE SPEED

Examples:

1. A pupil left home 7.25am and arrived school at 8.15am. If the distance from home to school is 2 ½ km, find the average speed of the car.

Solution

Distance = 2½ km                   Time = 7.25am to 8.15am

 

 

 

Convert 50minutes to hours = 50 ÷ 60 = 5/6 hrs

Speed = distance ÷ time

=

 

=  =  = 3km/hr

2. A man started a journey in his car at 8.00am. After 70km, he rested for 30min. he later continued for another 50km and ended his journey at 10.30am. Find the average speed of his car.

Solution

Total distance of the journey = 70km + 50km  = 120km

Time taken from 8.00am to 10.30am

Time taken to rest = 30minutes

Total time for the journey = 2hrs 30min – 30minutes = 2hrs

Average speed = distance  time = 120  2 = 60km/hr

Examples:

1. Adeolu walks a distance of 5km in 1 hour. How many kilometers will he walk in:
2. 2 hours    2 ½ hours

Solution:

Adeolu walks 5km in 1 hour.

1. In 2 hours he walks 5 x 2km = 10km
2. In 2 ½ hours he walks 5 x 2 ½ km = 5 x   5 km  =  25 km  =  12 ½ km

1         2              2

2. If Oluwole travels a distance of 28km in 4 hours on his bicycle, find his average speed in kilometers per hour.

Solution:

The total distance travelled is 28 km

The total time taken is 4 hours

Hence, Oluwole’s average speed = Total distance travelled (in km)

Total time taken (in hours)

= 28 km

4 hours      = 7km/h.   (or 7kmh^-1)

 

3. A car travelled 270 km in a time of 3 hours. Find the average speed.

Solution:

The total distance travelled  =  270km

Total time taken = 3 hours

 

Average speed = 270 km

3 hours              = 90km/h.  (or 90kmh^-1)

Speed (km/h or kmh-1)  =  Distance covered or travelled in km

                                                Time taken in hour

Also, Time (in hour)        =  Distance in km

                                          Speed in km/h

And   Distance (in km)   =  [Time (in hour) x Speed (in kilometer per hour)] km/h

 

Examples:

1. A car travelled a distance of 200km at an average speed of 50 km/h. find the time taken to cover this distance.

Solution:

Distance travelled  =  200km

Average speed of the car  =  50km/h

Time  =  Distance travelled                      =                    200 km

Speed                                                        50 km/h

=  4 h

 

2. A motor cyclist travels 48km at 16km/h, find the time taken.

Solution:

Distance travelled by motor cyclist  =  48km

Speed of the car  =  16km/h

Time taken  =  Distance travelled         =              48 km

Speed                                       16km/h

= 3h

 

3. Find the distance covered by a car travelling at 65 km/h for 7 hours.

Solution:

The speed of the car  =  65km/h (kmh^-1)

Time taken to cover the distance  =  7 h

Distance travelled  =  Speed  x  Time

=  65km/h x 7h

=  455 km

Quiz

1. A bus driver took 5hours from Lokoja to Owerri a distance of 350km, and then from Owerri to Ibi a distance of 130km took him another 3hours. What is the average speed from Lokoja to Ibi?

The average speed of a taxi was 100km/hr. the journey took 3hours 45minutes, what distance was the journey?

School Owner? Looking for ready-made content and tools to save time and grow easily? Book a free demo session now

Get more class notes, videos, homework help, exam practice on Android [DOWNLOAD]

Get more class notes, videos, homework help, exam practice on iPhone [DOWNLOAD]