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132 SCIPAD - BIG IDEAS - BOOK 2
FORCES AND MOTION
Calculating Speed
Speed is a measure of how far an object can travel in a certain amount of time. We often use
kilometres per hour in everyday life. However, scientists use metres per second as it is a more
accurate measure of speed. To calculate speed, we need to know two variables - the distance
travelled and the time taken to travel that distance.
1. Calculate the speed of the following objects.
(a) A car travels 12 m in 3 seconds.
Formula =
Working =
Speed =
(units)
(f) A woman runs 100 m in 12 seconds.
Formula =
Working =
Speed =
(units)
(b) A girl runs 20 m in 5 seconds.
Formula =
Working =
Speed =
(units)
(g) A cat runs 50 m in 8 seconds.
Formula =
Working =
Speed =
(units)
(c) A fish swims 30 m in 80 seconds.
Formula =
Working =
Speed =
(units)
(h) A man runs 400 m in 160 seconds.
Formula =
Working =
Speed =
(units)
(d) A 4 000 m cycle ride takes 1 600 s.
Formula =
Working =
Speed =
(units)
(i) A kiwi walks 5 m in 20 seconds.
Formula =
Working =
Speed =
(units)
(e) A 2 000 m horse trek takes 2500 s.
Formula =
Working =
Speed =
(units)
(j) A baby crawls 4 m in 20 seconds.
Formula =
Working =
Speed =
(units)
1. A car travels 120 metres in 16 seconds. Calculate the speed of the car.
v = ∆d / ∆t
= 120 m / 16 s
= 7.5 m s-1
A Worked Example
v
=
speed (ms-1)
∆d
=
change in distance (m)
∆t
=
change in time (s)
v =
∆d
∆t
You should ALWAYS
show
•
formula
•
working
•
answer
•
units
The Δ symbol means ‘change’.
For example, Δd means change in distance.
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