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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

21. The airplane returns to St. Louis by the same route. Because the prevailing winds push the airplane along,

the return trip takes only 3.75 hours. What is the average speed for this trip?

731.2 Km/h

22. The airplane refuels in St. Louis and continues on to Boston. It travels at an average speed of 610 km/h. If

the trip takes 2.75 hours, what is the flight distance between St. Louis and Boston?

1677.5 Km

23. The speed of light is about 3.00 105 km/s. It takes approximately 1.28 seconds for light reflected from the

moon to reach Earth. What is the average distance from Earth to the moon?

3.84 x 105 Km

24. The average distance from the sun to Pluto is approximately 6.10 109 km. How long does it take light from the sun to reach Pluto? Use the speed of light from the previous question to help you.

2.03 x104 s

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