Ria reached her home late after school because she was
cycling at a slow speed whereas her friend Dia reached her home early because
she was cycling with greater speed compared to Ria.
In both these examples, the word ‘speed’ has been used.
Now, what does the term ‘speed’ mean in mathematics?
Speed means how fast
something is moving or able to move.
In mathematics, speed is measured as the distance
covered/travelled per unit time.
Units of Measurement of Speed
Distance is covered
in kilometers and time is in hours, then the unit of measurement of speed is
‘km’ per ‘hour’ or km/hr. If the distance is in meters and time is in minutes, then
speed is ‘m’ per ‘min’ or m/min.
Example: The speed of the car
is 150 kilometers per hour (150 km/h).
Illustration 1: A truck covers a distance of 224 km
between Agra and Jaipur in 4 hours. Find its average speed.
Solution: Average Speed = Total distance covered
/ Total time taken
= 224 km/4
Illustration 2: Find the speed and average speed of a
train, which leaves New Delhi at 6 p.m. and reaches Agra next day at 7 a.m. The
distance between the two places is 220 km and the total time for stoppage is 1
hour between these two places.
Solution: Total time taken = 7 p.m. to 7 a.m.
Time for stoppage = 1 hour
Actual time taken = 12 hours – 1
hour = 11 hour
Speed = Total distance covered /
Total time taken
= 220 km/11
Illustration 3: The speed of train is 108 km/h. Find
its speed in meters per second.
Solution: 1km = 1000m
Therefore 108 km = 108 x 1000 =108,000 m
1 hr. = 60 min
1 min = 60 sec
Therefore, 1 hr. = 60 x 60 = 3600 sec
Speed = Distance / Time =
108,000/3600 = 30 m/sec
Illustration 4: A bus travels at a speed 50 m/s. Find
its speed in km/h.
Solution: Distance travelled by bus in 1 sec =
Distance travelled by bus in 1
hr = 50 x 3600 m (1hr = 3600 sec)
1m = 1/1000km
Speed = 50 x 3600 / 1000 = 180