Page 124 - ICSE Math 6

10 Speed, Distance and Time

Key Concepts

• Speed • Conversion of Units of Speed
• Units of Speed

Speed
Maths Info
Speed of a body is defined as the distance covered by the body in unit
A spacecraft leaving the surface
time. For example, if a motorbike covers 120 km in 2 hours, then it of Earth, needs to be going

will cover 120 km, i.e., 60 km in 1 hour. So, its speed is 60 kilometres about 11 kilometres per second
2 to enter the orbit.
per hour.

Distance Distance
Thus, Speed = ⇒ (i) Distance = Speed × Time (ii) Time =
Time Speed
If a body covers equal distances in equal intervals of time, then its speed is said to be uniform otherwise
its speed is variable. For example,
(a) If a car covers 50 km in the first hour, 50 km in the second hour and so on, then its speed is
uniform.
(b) If a car covers 40 km in the first hour, 60 km in the second hour and 55 km in the third hour, then
its speed is variable.

Units of speed
If the distance covered is in kilometres (km) and the time taken is in hours (h), then the unit of speed
is kilometre(s) per hour written as km h –1

If the distance covered is in metres (m) and the time taken is in seconds (s), then the unit of speed is
–1
metre(s) per second written as m s .
–1
Example 1: A car covers a distance of 33 km in 30 minutes. What is its speed in km h ?
–1
Solution: To find the speed in km h , the distance covered should be in kilometres and the time
taken should be in hours.

1
Time = 30 minutes = h
2
Distance 33 km
–1
\ Speed = = = 33 × 2 km h = 66 km h –1
Time 1/2 h
–1
Example 2: The speed of a train is 125 km h . Find the distance covered by the train in 3 hours.
–1
Solution: Distance = Speed × Time = 125 km h × 3 h = 375 km
–1
Example 3: The speed of a motorbike is 42 km h . How long will it take to travel 56 km?
Distance 56 km 1
Solution: Time = = –1 = 1 h = 1 hour 20 minutes
Speed 42 km h 3

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