4.1 Speed
The aim of this lesson is to
be able to use the correct
formulas to calculate speed,
distance or time
Speed is the distance traveled per unit of time.
Speed (s) =
distance (d)
time (t)
Each variable measured by units:
Distance: meters (m), miles (mi)
Time:seconds (s), hours (hr), minutes (min)
Speed:
meters per second (m/s),
miles per hour (mi/hr),
kilometers per hour (km/hr)
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2 TYPES OF SPEED (Average, Constant)
A . Constant Speed is when the object covers equal
distances in equal amounts of time.
B . Average speed is the total distance traveled
divided by the total time. It can be calculated using the
following formula:
Average Speed is:
Total distance =
distance traveled
speed =
distance
time
all
over
Total time =
final time (end) minus
initial time (beginning)
4
Four Step Approach to Solving Problems
G.U.E.S.S.A.
Step 1 READ THE PROBLEM.
Draw a picture.
Step 2 IDENTIFY THE VARIABLES
Write down what you know. GIVEN
What are you trying to find? UNKNOWN
Step 3
WRITE FORMULA
EQUATION
Set up the formula.
(The formula should match the unknown.)
Step 4 PLUG IN THE NUMBERS.
SUBSTITUTE
DO THE MATH
SOLVE.
Check ANSWER with UNITS
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The 3 formulas for Speed, Time & Distance:
Distance
Speed =
Time
Solving for Speed
Distance
Time =
Distance = Speed x Time
Speed
Solving for Time
Solving for Distance
D
Remember them from
this triangle:
S
T
Reminder: How to change minutes to hours
15 mins÷ 60 = 0•25 hour
So: 3 hours 15 mins = 3•25 hours
30 mins ÷ 60 = 0•5 hour
So: 7 hours 30 mins = 7•5 hours
45 mins÷ 60 = 0•75 hour
So: 2 hours 45 mins = 2•75 hours
“A car traveled 110 km in 2 hours.” calculate the speed
Step 1
Read the problem.
Draw a picture.
110 km
2 hours
d=
t=
s=
Formula
Plug-in
Units, units, units!
Answer
8
“A car traveled 110 km in 2 hours.”
Step 2
Write down what you know. GIVEN
What are you trying to find? UNKNOWN
110 km
2 hours
d = 110 km
t = 2 hours
s=
Formula
Plug-in
Units, units, units!
Answer
9
“A car traveled 110 km in 2 hours.”
Step 3 Set up the formula.
FORMULA SHOULD MATCH THE UNKNOWN
s=
d = 110 km
t = 2 hours
s=
Formula
d
t
Plug-in
Units, units, units!
Answer
10
“A car traveled 110 km in 2 hours.”
Step 3
d = 110 km
t = 2 hours
s=
Formula
S=
Set up the formula. EQUATION
Plug-in
Answer
d
t
Units, units, units!
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“A car traveled 110 km in 2 hours.”
Step 4
Plug-in the numbers. SUBSTITUTE
AND SOLVE. CHECK UNITS
55 km/hr
Formula
d = 110 km
d
t = 2 hours
S=
s = 55 km/hr
t
Plug-in
Answer
S = 110 km S = 55 km/hr
2 hr
Units, units, units!
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A windsurfer travelled 28 km in 1 hour 45 mins.
Calculate his speed.
Speed =
=
Distance
Time
D
S
T
28
1•75
1 hour 45 mins
= 16 km/h
Answer: His speed was 16 km / hour
A salesman travelled at an average speed of 50 km/h for 2
hours 30 mins. How far did he travel?
D
Distance = Speed x Time
S
= 50 x 2•5
T
2 hour 30 mins
= 125 km
Answer: He travelled 125 km
A train travelled 555 km at an average speed of 60
km/hr. How long did the journey take?
Distance
Time =
Speed
=
555
60
=
9•25 hours
D
S
T
= 9 hours 15 mins
Answer: It took 9 hours 15 minutes
Practice
If
a runner runs 100 meters in
50 seconds, what is his
speed in meters per second?
How far could this runner run
in 25 seconds?
Speed

A rocket is traveling at 10 m/s. How long does it
take the rocket to travel 30 m?
Speed

A racecar is traveling at 85.0 m/s. How
far does the car travel in 30.0 s?
and Average speed
distance traveled over
(Total
total time)
Both do not involve direction.
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Average Speed

A car drives 100 meters in 5 seconds.
1s
2
3
4
5
100 m

What is the car’s average speed?
s = d/t
 s = (100 m) / (5 s) = 20 m/s

Average speed
Average speed
What is the difference
between speed and velocity?
Velocity has speed & direction.
55 mi/hr
All of these cars had
different velocities
because they were traveling in different directions.
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