Constant Velocity Review
𝑉=
1. Show the calculation of the velocity of each object and round answers to 1 decimal place.
a. Object A’s velocity
𝑥𝑓 −𝑥𝑖
𝑡𝑓 −𝑡𝑖
X (m)
A
8
b. Object B’s velocity
6
D
4
c. Object C’s velocity
d. Object D’s velocity
2
-2
-4
C
-6
2. Using the above graph, write the specific equation for each object. The general
equation is Xf = Vt + Xi
a. Object A
b. Object B
c. Object C
d. Object D
3. Use the above equations to predict the final position of each object at 25 seconds.
a. Object A
b. Object B
c. Object C
d. Object D
4. Use the information in # 1 to find the displacement of each object at 25s. ∆𝑥 = 𝑉𝑡
a. Object A
b. Object B
c. Object C
d. Object D
B
-8
2
4
6
8
10 t (s)
Average velocity is calculated by the total displacement divided by total time.
𝑥 −𝑥
𝑉𝑎𝑣𝑔 = 𝑡𝑓−𝑡 𝑖 This is very similar to the velocity found in #1 above.
𝑓
X (m)
𝑖
8
Average speed is calculated by the total distance travelled divided by the total
time it took to travel that distance.
6
4
Average velocity We will use the graph to the right 
2
The final position of the object is -1m
The initial position of the object is +3m
The displacement is -4m
-2
Xf = -1m
Xi = 3m
Δx = Xf - Xi = -1m – 3m = -4m
-4
Or displacement = +5m+0m-11m+2m = -4m
The time is 11s.
𝑥𝑓 − 𝑥𝑖
−1𝑚 − 3𝑚 −4𝑚
𝒎
𝑉𝑎𝑣𝑔 =
=
=
= −𝟎. 𝟑𝟔
𝑡𝑓 − 𝑡𝑖
11𝑠 − 0𝑠
11𝑠
𝒔
-6
-8
2
4
6
8
10 t (s)
Average speed
The total distance is 18 meters
distance = 18m
Or distance = 5m+0m+11m+2m = 18m
The total time is 11s
t = 11s
𝑆𝑎𝑣𝑔 =
𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒
=
18𝑚
11𝑠
= 𝟏. 𝟔𝟒
𝒎
𝒔
Practice – Use Constant Velocity Particle Model Worksheet 1 and find the average speed and average velocity of the
objects in #’s 1 and 2. Show all work.
#1 Average speed
#1 Average velocity
#2 Average speed
#2 Average velocity
Conversion of units
When solving physics problems the units of the given information should all be in S.I. base units. The S.I. units for each
variable is as follows: distance (displacement) = meter, time = second, speed (velocity) = meter/second. If the problem
gives you any of the previous information in units other than the above units, you must convert the information to the
S.I. base units.
Convert 26 minutes to seconds. The conversion factor is 1 minute for each 60 seconds. Multiply the given quantity by
the conversion factor where the desired units are in the top of the fraction, and the undesired units are cancelled out.
60𝑠
26𝑚𝑖𝑛 (1𝑚𝑖𝑛) = 𝟏𝟓𝟔𝟎𝒔
Notice how the minutes cancel out leaving seconds in the numerator.
Convert 11km/h to m/s. The conversion factor for distance is 1km for each 1000m, and the conversion factor for time is
1h for each 3600s.
11𝑘𝑚
1000𝑚
1ℎ
)(
)(
)
ℎ
1𝑘𝑚
3600𝑠
(
= 𝟑. 𝟏
𝒎
𝒔
Notice how km and h are cancelled out leaving the desired S.I. units.
Convert 55mph (miles per hour) to m/s This will not be tested, just for funsies
55𝑚𝑖 5280𝑓𝑡 12𝑖𝑛 2.54𝑐𝑚
1𝑚
1ℎ
𝒎
(
)(
)(
)(
)(
)(
) = 𝟐𝟒. 𝟔
ℎ
1𝑚𝑖
1𝑓𝑡
1𝑖𝑛
100𝑐𝑚 3600𝑠
𝒔
Steps for problem solving
1. Read the problem and draw a simple diagram to get a better idea.
2. Write down given or assumed information, and then identify the information as specific variables (Xf, t, V, etc.)
2. Identify which models apply to the question, or parts of the question. (Models include constant velocity, acceleration,
balanced or unbalanced forces, etc.)
3. Write down the equation that fits with the model, and solve the equation for the variable the question is asking for.
4. Plug in numbers and correctly enter them into your calculator.
5. Once you have your answer, ask yourself if it makes sense (sometimes you won’t be able to) or check your answer
Check your answer – take your answer and plug it back into an equation and solve for a given quantity. If you get the
given quantity, or very close then you are correct. If not then look for some potential sources of error
Potential sources of error –Solve the equation correctly? Enter it into your calculator correctly? Identify given
information correctly? Did you convert units correctly? Use the correct equation? The first 3 are the most common
mistakes.
Word Problems – Practice Use the above steps in solving the below problems.
1. Heather and Matthew walk eastward with a speed of 0.98 m/s. If it takes them 34 min to walk to the store, how far
have they walked?
2. If Joe rides south on his bicycle in a straight line for 15 min with an average speed of 12.5 km/h, how far has he
ridden?
3. It takes you 9.5 min to walk with an average velocity of 1.2 m/s to the north from the bus stop to the museum
entrance. What is your displacement?
4. Simpson drives his car with an average velocity of 48 km/h to the east. How long will it take him to drive 144 km on a
straight highway?
5. How much time would Simpson save (in #4) by increasing his average velocity to 56 km/h to the east?
6. A bus travels 280 km south along a straight path with an average velocity of 88 km/h to the south. The bus stops for
24 min, then it travels 210 km south with an average velocity of 75 km/h to the south.
a. How long does the total trip last?
b. What is the average velocity for the total trip?