Chapter 9 Speed ANSWERS Name:
Period:
Date:12.2
Speed
To determine the speed of an object, you need to know the distance
traveled and the time taken to travel that
distance. However, by rearranging the formula for speed, v =
d/t, you can also determine the distance traveled or
the time it took for the object to travel that distance, if you
know the speed. For example,
EQUATION
GIVES YOU
IF YOU KNOW
v=d/t
Speed
Distance time
d = v x t
Distance
Speed and time
t = d/v
Time
Distance and speed
Use the SI system to solve the practice problems unless you are
asked to write the answer using the English
system of measurement. As you solve the problems, include all
units and cancel appropriately.
EXAMPLES
Example 1: What is the speed of a
cheetah that travels 112.0 meters in 4.0 seconds?Eqation... Gives you... Looking for: Solution: speed = d/t
Speed of the cheetah.
112.0 m / 4.0 s = 28 m/s
The
speed of the cheetah is 28 meters per second.
Given
Distance = 112.0 meters
Time = 4.0 seconds
Relationship
speed = d/t
Example 2: There are 1,609 meters in
one mile. What is this cheetah’s speed in miles/hour?
Looking for : Solution:
Speed of the cheetah in miles per hour 28m
1 mile 3600 s
63 miles
x x
=
Given s
1609 m 1 hour hour
Distance = 112.0 meters
Time = 4.0 seconds The
speed of the cheetah in miles per hour is 63 mph
Relationships
speed = d/t and 1,609 meters = 1 mile
12.2
1. A bicyclist travels 60.0 kilometers in 3.5 hours. What is the
cyclist’s average speed?
17.74Km/h
2. What is the average speed of a car that traveled 300.0 miles in
5.5 hours?
54.55
mi/h
3. How much time would it take for the sound of thunder to travel
1,500 meters if sound travels at a speed of
330 m/s?
4.55
s
4. How much time would it take for an airplane to reach its
destination if it traveled at an average speed of 790 kilometers/hour for a
distance of 4,700 kilometers? What is the airplane’s speed in miles/ hour?
6.27h 465.84 Km/h
5. How far can a person run in 15 minutes if he or she runs at an
average speed of 16 km/hr?
(HINT: Remember to convert minutes to hours.)
4
Km
6. In problem 5, what is the runner’s distance traveled in miles?
2.48
mi
7. A snail can move approximately 0.30 meters per minute. How many
meters can the snail cover in
15 minutes?
4.5
m
8. Calculate the average speed (in km/h) of a car stuck in traffic
that drives 12 kilometers in 2 hours.
6
Km/h
9. How long would it take you to swim across a lake that is 900
meters across if you swim at 1.5 m/s? 12.2
a. What is the answer in seconds?
600
s
b. What is the answer in minutes?
100
min
11. How far will you travel if you run for 10 minutes at 2 m/s?
1200
m
12. You have trained all year for a marathon. In your first
attempt to run a marathon, you decide that you want to complete this 42 meter
race in 4.5 hours.
a. What is the length of a marathon in kilometers
0.042
Km
b. What would your average speed have to be to complete the race
in 4.5 hours? Give your answer in kilometers per hour.
0.0093
Km/h
13. Suppose you are walking home after school. The distance from
school to your home is five kilometers. On
foot, you can get home in 25 minutes. However, if you rode a
bicycle, you could get home in 10 minutes.
a. What is your average speed while walking? 0.2 Km/min
b. What is your average speed while bicycling? 0.5 Km/min
c. How much faster you travel on your bicycle? 0.3 Km/min
14. Suppose you ride your bicycle to the library traveling at 0.5
km/min. It takes you 25 minutes to get to the library. How far did you travel?
12.5
m
15. You ride your bike for a distance of 30 km. You travel at a speed
of 0.75 km/ minute. How many minutes does this take?
40
min
16. A train travels 225 kilometers in 2.5 hours. What is the
train’s average speed?
90
Km/h
17. An airplane travels 3,260 kilometers in 4 hours. What is the
airplane’s average speed?
815
Km/h
18. A person in a kayak paddles down river at an average speed of
10 km/h. After 3.25 hours, how far has she
traveled?
32.5
Km
19. The same person in question 18 paddles upstream at an average
speed of 4 km/h. How long would it take her to get back to her starting point?
8.14
h
20. An airplane travels from St. Louis, Missouri to Portland,
Oregon in 4.33 hours. If the distance traveled is
2,742 kilometers, what is the airplane’s average speed?
633.26
Km/h
