# AP FR Quiz #1 Motion

```AP QUIZ #1 MOTION
1) BALL STROBE DIAGRAMS—SPEED
The following drawings represent strobe (flash) photographs of a ball moving in the direction of the arrow. The circles represent the
positions of the ball at succeeding instants of time. The time interval between successive positions is the same in all cases.
A
B
C
D
Rank each case based on the magnitude of the ball's average speed in the last time interval.
OR
1
Greatest
2
3
4
Least
All
the same
All
zero
Cannot
determine
Answer: A = D > B > C.
Since the time intervals are the same in all cases, the distance between any two adjacent positions of the ball will be proportional
to the average speed of the ball in the time interval between when those photographs were taken. By comparing the spacing
between the last two positions for each case we can determine the average speed in the last time interval.
1) Ball Strobe Diagrams—Acceleration I
The following drawings represent strobe (flash) photographs of a ball moving in the direction of the arrow. The circles represent the
positions of the ball at succeeding instants of time. The time interval between successive positions is the same in all cases. Assume
all accelerations are constant.
A
B
C
D
Rank the magnitude of the acceleration for each case based on the drawings.
OR
1
Greatest
2
3
4
Least
All
the same
All
zero
Cannot
determine
Answer: B = D > A > C.
The spacing of the successive position changes given determine the direction of the acceleration and give an indication of the
relative magnitude of the acceleration. In cases B and D, the acceleration is the same, in the direction of the arrow, and fairly
large, because the speed of the ball is increasing quite a bit in each time interval.
In case A the acceleration points opposite to the direction of the arrow and has a slightly smaller magnitude than B and D. In
case C, the acceleration is zero since the ball has a constant direction and rate of motion.
3) BALL STROBE DIAGRAMS—ACCELERATION II
The following drawings represent strobe (flash) photographs of a ball moving in the direction of the arrow. The circles represent the
positions of the ball at succeeding instants of time. The time interval between successive positions is the same in all cases. Assume
all accelerations are constant.
A
B
C
D
Rank the magnitude of the acceleration in each case, based on the drawings.
OR
1
Greatest
2
3
4
Least
All
the same
All
zero
Cannot
determine
Answer: B = D > A > C. The acceleration is the rate of change of the velocity. Since the velocity of C is constant the acceleration
is zero for that case. For the others we can look at the changes in the average velocities, which are proportional to the changes
in the spacing between successive locations. These are equivalent for B and D, but A has a smaller magnitude acceleration.
B1-RT04: Strobe Photographs of Spheres—Displacement
In each case, a sphere is moving from left to right next to a tape marked in meters. A strobe (flash) photograph is taken every
second, and the location of the sphere is recorded. The total time intervals shown are not the same for all spheres.
A
B
C
D
0
1
2
3
4
5
6
7
8
9
10 m
0
1
2
3
4
5
6
7
8
9
10 m
0
1
2
3
4
5
6
7
8
9
10 m
0
1
2
3
4
5
6
7
8
9
10 m
Rank these spheres on the greatest displacement over the first 3 seconds.
OR
1
Greatest
2
3
4
Least
All
the same
All
zero
Cannot
determine
Answer: C = D > A > B. The displacements for C and D during the first three seconds was 9 m, next was A at 6 m and least is B
at 2 m.
4) STROBE PHOTOGRAPHS OF SPHERES—AVERAGE VELOCITY
In each case, a sphere is moving from left to right next to a tape marked in meters. A strobe (flash) photograph is taken every
second, and the location of the sphere is recorded. The total time intervals shown are not the same for all spheres.
A
B
C
D
0
1
2
3
4
5
6
7
8
9
10 m
0
1
2
3
4
5
6
7
8
9
10 m
0
1
2
3
4
5
6
7
8
9
10 m
0
1
2
3
4
5
6
7
8
9
10 m
Rank these spheres on the greatest average velocity over the first 3 seconds.
OR
1
Greatest
2
3
4
Least
All
the same
All
zero
Cannot
determine
Answer: C = D > A > B. Average velocity is defined as the displacement during a time interval divided by the time interval. The
time interval is the same for all four cases, so the average velocities are determined by the displacements, which are proportional
to the distances traveled in the first three seconds.
5) Vertical Model Rockets—Maximum Height
The model rockets depicted below have just had their engines turned off when they are at the same height. All of the rockets are
aimed straight up, but their speeds differ. Although they are the same size and shape, the rockets carry different loads so their
masses differ. The specific mass and speed for each rocket is given in each figure.
A
B
C
D
30 m/s
40 m/s
20 m/s
20 m/s
700 g
500 g
600 g
500 g
Rank these model rockets on the maximum height they will reach.
OR
1
Greatest
2
3
4
Least
All
the same
All
zero
Cannot
determine
Answer: B > A > C = D. All four experience the same acceleration of 9.8 m/s2 downward, so their maximum heights are
determined by their speed. Ignoring air resistance all objects have the same acceleration in the Earth’s gravitational field
whatever their masses.
6) Change of Velocity
In each figure below, a car’s velocity is shown before and after a short time interval.
A
C
Before
After
+10 m/s
+20 m/s
Before
After
+10 m/s
-10 m/s
B
D
Before
After
+10 m/s
0
Before
+30 m/s
After
+20 m/s
Rank these situations on the magnitude of the change in velocity during the time interval.
OR
1
Greatest
2
3
4
Least
All
the same
All
zero
Cannot
determine
Answer: C > A = B = D. The magnitude of the change in velocity for C is 20 m/s while the other three all have 10 m/s velocity
changes.
7) PEOPLE ON TRAINS—SPEED RELATIVE TO GROUND
In each case shown, someone is running on a flatbed train car as the train moves. In cases C and D, the person is running toward the
front of the train, while in cases A and B the person is running toward the rear. The speeds of the train and of each person relative to
the train are given. An observer is standing beside the track watching each train go by.
A
B
vP = 8 m/s
vP = 10 m/s
vT = 30 m/s
vT = 24 m/s
C
vP = 12 m/s
D
vP = 4 m/s
vT = 20 m/s
vT = 16 m/s
Rank these runners on how fast they are moving relative to the observer standing beside the tracks.
OR
1
Greatest
2
3
4
Least
All
the same
All
zero
Cannot
determine
Answer: C > B = D > A. The observer would see the runner moving at 32 m/s in C, 20 m/s in B and D, and 16 m/s in A.
8) Moving Asteroids near Observer Spaceship—Velocity Direction
Shown are five asteroids and a spaceship, all moving in the same direction away from the earth. The velocities of the asteroids and
of the spaceship are given as measured from the earth.
A
B
C
D
600 m/s
700 m/s
800 m/s
400 m/s
E
400 m/s
600 m/s
(1) List the asteroids that are moving toward an observer on the spaceship.
B and C and E
(2) List the asteroids that are moving away from an observer on the spaceship.
D.