Motion in Our World
3.5
Average Speed Formula
Part One: Analyzing the Formula
1. Quick Questions:
a) What UNIT do we use for “distance”?
b) What does “t” mean?
c) How do we convert from “km” into “m”?
d) What does the “Δ” mean?
e) How do we convert from “m” into “km”?
f) What UNIT do we use for “speed”?
g) How do we convert from “km/h” into “m/s”?
2. Find-the-mistakes!
Below, you see a typical science question and 3 student solutions of the same question.
The question:
The speed of the average human sneeze is 115 km/h (31.94 m/s). If you are sitting
2 m away from the person who is about to sneeze, how long do you have to react,
once he/she sneezes?
Here are the three soluitons:
Solution #1:
Solution #2:
Solution #3:
a) List 3 things that all students did correctly as they solved the question.
b) Only one of solutions is solved correctly. Which one? How do you know?
c) Each of the other two has a mistake. Identify the error each student made as they
solved.
d) Explain WHY it was valuable that the students “showed their work” (and why you’ll
always be asked to do the same).
Part Two: Putting It Together
For each of these, please make sure you “show your work”, which involves:
1. Writing the numbers
2. Showing the formula you’re going to use
3. Substituting the numbers
4. Solving (and circling the answers)
1. A car and a truck travel along the same highway with the car moving faster than the truck.
a) How do their distances compare after they travel the same length of time?
b) After traveling the same distance, how does their time compare?
2. How fast is a person traveling (in m/s) if he or she is traveling 90 km/h?
3. If two hikers walk the Trans Canada Trail for 6.0 h, and cover 31 km, what is their average
speed for the day?
4. The “hand” of the CanadArm [at left] used on the space shuttle can move up to
0.6 m/s without carrying anything. What is the minimum time for the
CanadArm’s hand to move 1.20 m?
5. According to Google Maps, the distance from Spiritwood, SK to Edmonton, AB is
510.3 km. If a person travelled that distance in 5.5 hours, what is the person’s
average speed during the trip? Is he or she speeding?
6. The fastest land-speed record was set in 1997 by the Thrust
SSC (a jet-engine car [picture at right]), which traveled 604 m
at an average speed of 341 m/s. How long did it take the car to travel that
far? (http://en.wikipedia.org/wiki/Land_speed_record)
7. The cruise control of a car is set at 90 km/h. The car travels at this
constant average speed before running out of gas and stopping exactly 2
hours 12 min after starting. If the total trip is 200 km, how far will the driver still have to go
to finish the trip?
8. The Bretiling Orbiter 3 balloon [at right] set world
records in 1999 by travelling 40 814 km in 19 d, 21 h,
and 47 min, flying over the Swiss Alps. Calculate the
average speed of the balloon.
______________________________________________________________________________
Answers to “Putting It Together”:
1a) which travels further? Why?
3) 1.44 m/s
4) 0.5 s
7) 198000 m (or 198 km), so 2000 m more (2 km)
1b) which takes less time? Why?
2) 25 m/s
5) 25.77 m/s
6) 1.77 s
8) convert the time into “seconds” first… answer = 23.72 m/s