22 Rate
By studying this lesson you will be able to
• solve problems related to distance, time and speed
• represent information related to distance and time graphically
• solve problems related to liquid volumes, time and rate.
22.1 Speed
A 10 m B
Let us assume that a battery operated toy car takes 5 seconds to travel from point A
to point B which is 10 m away.
Then the distance that the car has travelled during 5 seconds is 10 m. If the distance
that the car moves forward during each second is the same from the moment it
starts, then the distance it travels during each second is metres, that is, 2 metres.
Accordingly, as the car moves forward from A, the rate at which the distance
changes with respect to time is 2 metres per second. We can define this value as the
speed with which the car travels from A to B.
If the distance travelled by an object in motion is a constant per unit of time, then the
object is said to be travelling with uniform speed. Further, the speed of the object is
then the distance travelled per unit of time. From this point on, only objects which
travel with uniform speed will be considered in this lesson.
However, in reality, vehicles that travel on the main road are usually unable to
maintain a uniform speed throughout the whole journey due to the traffic on the
road and various other reasons. The instrument called the speedometer gives the
speed of a vehicle at any given instance.
The speed denoted by the speedometer in the figure can be
written as 80 kmph. It can also be written as 80 km /h or
as 80 kmh–1.
For free distribution 43
, As you travel along a main road, you may observe road signs with 40 kmph and 60
kmph written on them to indicate speed limits. Try to recall that heavy vehicles such as
lorries carry a board at the back with 40 kmph written on it.
For an object that is moving with uniform speed, the relationship between the
three quantities, namely the distance travelled, the time taken and the speed can be
written as follows.
Speed = Distance travelled
Time taken
This relationship can also be written in the following simple form (without fractions).
Distance = Speed « Time
Example 1
A feather floating on air with uniform speed, drifts 100 m in 20 seconds. Calculate
the speed with which the feather drifts.
Distance it drifts
Speed with which it drifts =
time
Example 2
Calculate the distance travelled in one minute by a bird that flies at a uniform speed
of 5 ms-–1.
Distance it flies = speed « time
= 5 ms-–1 « 60 s
= 300 m
44 For free distribution
By studying this lesson you will be able to
• solve problems related to distance, time and speed
• represent information related to distance and time graphically
• solve problems related to liquid volumes, time and rate.
22.1 Speed
A 10 m B
Let us assume that a battery operated toy car takes 5 seconds to travel from point A
to point B which is 10 m away.
Then the distance that the car has travelled during 5 seconds is 10 m. If the distance
that the car moves forward during each second is the same from the moment it
starts, then the distance it travels during each second is metres, that is, 2 metres.
Accordingly, as the car moves forward from A, the rate at which the distance
changes with respect to time is 2 metres per second. We can define this value as the
speed with which the car travels from A to B.
If the distance travelled by an object in motion is a constant per unit of time, then the
object is said to be travelling with uniform speed. Further, the speed of the object is
then the distance travelled per unit of time. From this point on, only objects which
travel with uniform speed will be considered in this lesson.
However, in reality, vehicles that travel on the main road are usually unable to
maintain a uniform speed throughout the whole journey due to the traffic on the
road and various other reasons. The instrument called the speedometer gives the
speed of a vehicle at any given instance.
The speed denoted by the speedometer in the figure can be
written as 80 kmph. It can also be written as 80 km /h or
as 80 kmh–1.
For free distribution 43
, As you travel along a main road, you may observe road signs with 40 kmph and 60
kmph written on them to indicate speed limits. Try to recall that heavy vehicles such as
lorries carry a board at the back with 40 kmph written on it.
For an object that is moving with uniform speed, the relationship between the
three quantities, namely the distance travelled, the time taken and the speed can be
written as follows.
Speed = Distance travelled
Time taken
This relationship can also be written in the following simple form (without fractions).
Distance = Speed « Time
Example 1
A feather floating on air with uniform speed, drifts 100 m in 20 seconds. Calculate
the speed with which the feather drifts.
Distance it drifts
Speed with which it drifts =
time
Example 2
Calculate the distance travelled in one minute by a bird that flies at a uniform speed
of 5 ms-–1.
Distance it flies = speed « time
= 5 ms-–1 « 60 s
= 300 m
44 For free distribution
