Activity 9.2 – Velocity and Acceleration
In this activity you will interpret a position- time and velocity- time graph.
Part 1: Interpreting a Position-Time Graph
All question for Part 1 are based on this graph:
Motion of Three Vehicles
35
30
Position m [N]
25
20
15
Car A
Car B
10
Car C
5
0
0
-5
10
20
30
Time (s)
40
50
60
-10
1) Recall that distance is the length of the path the object took.
Displacement only looks at where the object started and where it ended
up; the path does not matter.
Keeping this in mind, compare the distance and displacement of the 3
cars from 0 s to 20 s.
Car A
Car B
Car C
Distance (m)
30
25
35
Displacement (m) 30
25
-5
2) Describe the motion of Car A, B and C in words.
3) Recall that the slope of a Position-Time graph is the velocity. Fill in the
chart below using “+”, “-“, or “0” for velocity
Time Interval
0-10 s
20-30 s
50-60 s
Car A Velocity
+
+
+
Car B Velocity
+
0
+
Car C Velocity
+
+
-
Part 2: Interpreting A Velocity – Time Graph
All questions for Part 2 area based on this graph:
Velocities of Three Cars
0.6
0.4
Velocity (m/s2)
0.2
0
-0.2
0
10
20
Time (s)
30
40
-0.4
-0.6
50
60
Car A
Car B
Car C
-0.8
-1
-1.2
***note these are the same 3 cars from Part 1***
1) What is the slope of the lines on this velocity –time graph equivalent to?
Acceleration
2) Car A only has a slope when it goes from rest to 0.5 m/s. It then shows
zero slope. What type of motion is this from 0-5s? Uniform motion
3) What does zero slope mean on a POSITION-time graph (Part 1)? What
does zero slope mean on a VELOCITY-time graph? Not moving, moving
at a constant velocity
4) Describe the motion of Car C from 40 to 50 s? The car is moving in a
backwards direction, speeding up.
5) What is Car C’s acceleration (look at the slope) from 40 to 50 s (positive,
negative or zero)? negative
6) Describe the motion of Car C from 50 to 60 s? going backwards but
slowing down.
7) What is Car C’s acceleration (look at the slope) from 50 to 60 s (positive,
negative or zero)? Positive
8) Fill in the chart below with the correct sign of the acceleration in each
situation (+. – or 0)
Direction
Forward (+)
Forward (+)
Backwards (-)
Backwards (-)
Velocity
Speeding up
Slowing down
Speeding up
Slowing down
Acceleration
+
+
9) In general, what can be said about the signs of the acceleration and
velocity if:
a. The object is speeding up ? (velocity and acceleration match)
b. The object is slowing down? (velocity and acceleration have
opposite signs)
Part 3: Falling Objects
1) A ball is thrown in the air. The position of the ball is shown in the data below.
Graph a POSITION – TIME graph for the ball.
Time (s)
0
1
2
3
4
Position (m)
0
14.7
19.6
14.7
0
Make a “best fit” line graph. Best fit means you draw a smooth line that goes
through most of the points, not a “connect the dots” line. Scan your graph and
upload with this assignment
Tips for good graphing:
- use a ruler for straight lines,
- make sure to label all axis including units,
- make sure all intervals (the squares or tic marks on a graph) are worth an
EQUAL AMOUNT...for example go up by twos, fives etc.
- the graph should be large enough to be interpreted visually....at least 1/2 a
page is a good rule of thumb
Motion of a Thrown ball
25
Position m [up]
20
15
10
5
0
0
-5
1
2
3
4
5
Time (s)
1) What is causing this ball to slow down? Gravity
2) What is the ball’s velocity and acceleration at 3 s? Explain how you know.
Velocity is zero (slope of line), acceleration must be zero (acceleration is
change in velocity over time).
3) On separate piece of paper, answer the following questions. SHOW ALL
YOUR WORK…this means the formula, math and answer with units.
Scan your work and upload with this assignment
a. Find displacement of the ball from 0 to 4 seconds. 0 m
b. Find the average velocity of the ball from 0 to 2 seconds. 9.8 m/s
c. Find the acceleration from 0 to 2 seconds. -9.8 m/s2
How would you know if you answer for 3c makes sense? The
acceleration is due to gravity and should be -9.8 m/s2
Reminder: upload your word document, graph and calculations for
this assignment.