CLASS NOTES
CLASS : 8
SUBJECT : MATHEMATICS
CHAPTER : SPEED, TIME AND DISTANCE
”Building Strong Concepts Today for Tomorrow’s IIT and Olympiad Success.”
Contents
Definitions
Speed: Speed of an object is the distance travelled by it per unit time.
Distance
Speed =
Time
Distance: Distance is the total length of the path travelled by an object.
Distance = Speed × Time
Time: Time is the duration for which an object is in motion.
Distance
Time =
Speed
Uniform Speed: An object is said to be moving with uniform speed if it covers equal
distances in equal intervals of time.
Variable Speed: An object is said to be moving with variable speed if it covers unequal
distances in equal intervals of time.
Average Speed: Average speed is defined as the total distance travelled divided by the total
time taken.
Total Distance Travelled
Average Speed =
Total Time Taken
, Relative Speed: Relative speed of one object with respect to another is the speed of one
object as observed from the other object.
Train Passing Problems:
• When a train passes a pole or a standing man, the distance covered is equal to the length
of the train.
• When a train passes a platform, bridge or tunnel, the distance covered is equal to the sum
of the length of the train and the length of the platform, bridge or tunnel.
• When two trains pass each other (in same or opposite direction), the distance covered is
equal to the sum of the lengths of both the trains.
Example 1
A boy runs 900 metres in 6 minutes.
(i) Find his speed in m/sec and in km/hr.
(ii) How much distance will he cover in 2 12 hours?
(iii) How much time will he take to cover 3 km?
Solution.
(i) Distance covered = 900 metres, time taken = 6 minutes = (6 × 60) seconds = 360 seconds.
900 m
Speed = = 2.5 m/sec.
360 sec
In km/hr, speed = 2.5 × 18
5 km/hr = 9 km/hr.
(ii) Distance covered in 2 21 hours
= Speed × Time = (9 km/hr) × 2.5 = 22.5 km.
(iii) Time required to cover 3 km
Distance 3 1
= = hr = hr = 20 minutes.
Speed 9 3
CLASS : 8
SUBJECT : MATHEMATICS
CHAPTER : SPEED, TIME AND DISTANCE
”Building Strong Concepts Today for Tomorrow’s IIT and Olympiad Success.”
Contents
Definitions
Speed: Speed of an object is the distance travelled by it per unit time.
Distance
Speed =
Time
Distance: Distance is the total length of the path travelled by an object.
Distance = Speed × Time
Time: Time is the duration for which an object is in motion.
Distance
Time =
Speed
Uniform Speed: An object is said to be moving with uniform speed if it covers equal
distances in equal intervals of time.
Variable Speed: An object is said to be moving with variable speed if it covers unequal
distances in equal intervals of time.
Average Speed: Average speed is defined as the total distance travelled divided by the total
time taken.
Total Distance Travelled
Average Speed =
Total Time Taken
, Relative Speed: Relative speed of one object with respect to another is the speed of one
object as observed from the other object.
Train Passing Problems:
• When a train passes a pole or a standing man, the distance covered is equal to the length
of the train.
• When a train passes a platform, bridge or tunnel, the distance covered is equal to the sum
of the length of the train and the length of the platform, bridge or tunnel.
• When two trains pass each other (in same or opposite direction), the distance covered is
equal to the sum of the lengths of both the trains.
Example 1
A boy runs 900 metres in 6 minutes.
(i) Find his speed in m/sec and in km/hr.
(ii) How much distance will he cover in 2 12 hours?
(iii) How much time will he take to cover 3 km?
Solution.
(i) Distance covered = 900 metres, time taken = 6 minutes = (6 × 60) seconds = 360 seconds.
900 m
Speed = = 2.5 m/sec.
360 sec
In km/hr, speed = 2.5 × 18
5 km/hr = 9 km/hr.
(ii) Distance covered in 2 21 hours
= Speed × Time = (9 km/hr) × 2.5 = 22.5 km.
(iii) Time required to cover 3 km
Distance 3 1
= = hr = hr = 20 minutes.
Speed 9 3
