Download Boxcars and Ropes—Stopping Force in Same Distance 56 In a

Boxcars and Ropes—Stopping Force in Same Distance 56
In a western movie, a confederate raiding party stopped a runaway boxcar carrying gold by using many
ropes tied to trees. Given below are six boxcars that are moving along horizontal railroads at specified
speeds. Also given are the masses of the boxcars. All of the boxcars are the same size and shape, but they
are carrying loads with different masses. All of these boxcars are going to be stopped by plowing through a
large number of these secured ropes. All of the boxcars need to be stopped in the same distance.
Rank these situations from greatest to least on the basis of the strength of the forces that will be needed to
stop the boxcars in the same distance. That is, put first the boxcar on which the strongest force will have
to be applied to stop it in x meters, and put last the boxcar on which the weakest force will be applied to
stop the boxcar in the same distance.
4 m/s
A
5 m/s
Boxcar
Boxcar
10 Mg
6 m/s
D
16 Mg
5 m/s
10 m/s
E
F
Boxcar
Boxcar
10 Mg
16 Mg
12 Mg
C
Boxcar
12 Mg
Boxcar
Greatest
10 m/s
B
1 _______ 2 _______ 3 _______ 4 _______ 5 _______ 6 _______
Least
Or, all boxcars require the same force. __________
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
56
7
8
Very Sure
9
10
T. O’Kuma
Physics Ranking Tasks
60
Mechanics
Cars and Barriers—Stopping Distance with the Same Force 58
Shown below are eight cars that are moving along horizontal roads at specified speeds. Also given are the
masses of the cars. All of the cars are the same size and shape, but they are carrying loads with different
masses. All of these cars are going to be stopped by plowing into identical barriers. All of the cars are
going to be stopped by the same constant force by the barrier.
Rank these situations from greatest to least on the basis of the stopping distance that will be needed to
stop the cars with the same force. That is, put first the car that requires the longest stopping distance and
put last the car that requires the shortest distance to stop the car with the same force.
10 m/s
A
m = 1000 kg
10 m/s
E
m = 2000 kg
20 m/s
30 m/s
B
m = 1000 kg
20 m/s
10 m/s
C
m = 1000 kg
30 m/s
F
m = 2000 kg
D
m = 3000 kg
20 m/s
H
G
m = 3000 kg
m = 2000 kg
Longest 1 _____ 2 _____ 3 _____ 4 _____ 5 _____ 6 _____ 7 _____ 8 _____ Shortest
Or, all the cars require the same distance. __________
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
58
7
8
Very Sure
9
10
T. O’Kuma, D. Maloney, C. Hieggelke
Physics Ranking Tasks
62
Mechanics
Cars—Work Done in Change of Velocity 59
The eight situations below show before and after "snapshots" of a car's velocity. Rank these situations, in
terms of work done on the car, from most positive to most negative, to create these changes in velocity for
the same distance traveled. All cars have the same mass. Negative numbers, if any, rank lower than
positive ones (-20 m/s < -10 m/s < 0< 5).
BEFORE
AFTER
A
BEFORE
AFTER
+20 m/s
+30 m/s
+30 m/s
+20 m/s
-10 m/s
-20 m/s
+30 m/s
-20 m/s
E
+10 m/s
+20 m/s
B
F
+10 m/s
0 m/s
C
G
+10 m/s
-10 m/s
D
H
+20 m/s
+20 m/s
Most
Most
Positive 1_____ 2_____ 3_____ 4_____ 5_____ 6_____ 7_____ 8_____ Negative
Or, the work done on the cars is the same (but not zero) for all of these. _________
Or, the work done on the cars is zero for all of these. _________
Or, it is not possible to determine the work done on the cars for all these cases. _________
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
59
7
8
Very Sure
9
10
J. Cole, D. Maloney
Physics Ranking Tasks
63
Mechanics
Bouncing Cart—Work Done by the Barrier
61
A cart with a spring plunger runs into a fixed barrier. The mass of the cart, its velocity just before impact
with the barrier, and its velocity right after collision are given in each figure.
Rank the work done by the barrier on each cart from the greatest work done by the barrier to the least work
done by the barrier ( + direction is to the right and - to the left with –4 < -2).
Before
10 kg
After
A
v o = 4 m/s
10 kg
10 kg
After
B
v o = 5 m/s
20 kg
v o = 2 m/s
10 kg
20 kg
v f = -1 m/s
C
D
20 kg
vf = 0 m/s
v o = 3 m/s
5 kg
Before
vf = 0 m/s
E
vo = 1 m/s
5 kg
10 kg
v f = -3 m/s
20 kg
v f = -1 m/s
F
v o = 2 m/s
10 kg
vf = -2 m/s
Greatest 1_______ 2________ 3________ 4________ 5________ 6________ Least
Or, the work done by the barriers is the same for all these cases.
Or, there is no work done by the barrier for all these cases.
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
61
7
8
Very Sure
9
10
T. O’Kuma, C. Hieggelke
Physics Ranking Tasks
65
Mechanics
Model Rockets—Kinetic Energy 63
The eight figures below depict eight model rockets that have just had their engines turned off. All of the
rockets are aimed straight up, but their speeds differ. All of the rockets are the same size and shape, but
they carry different loads, so their masses differ. The mass and speed for each rocket is given in each
figure. (In this situation we are going to ignore any effect air resistance may have on the rockets.) At the
instant when the engines are turned off, the rockets are all at the same height.
Rank these model rockets from greatest to least on the basis of the kinetic energy they have at the top of
their flights.
A
30 m/s
B
700 g
E
30 m/s
400 g
40 m/s
500 g
F
40 m/s
C
D
20 m/s
700 g
600 g
G
600 g
20 m/s
H
30 m/s
20 m/s
500 g
600 g
Greatest 1_____ 2_____ 3_____ 4_____ 5_____ 6_____ 7_____ 8______ Least
Or, all rockets have the same kinetic energy.___________
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
63
7
8
Very Sure
9
10
T. O’Kuma, D. Maloney
Physics Ranking Tasks
67
Mechanics
Sliding Masses on Incline—Kinetic Energy 64
Rank, in order from greatest to least, the final kinetic energies of the sliding masses the instant before
they reach the bottom of the incline. All surfaces are frictionless. All masses start from rest.
1 kg
10 kg
A
D
10 m
1m
2m
5m
10 kg
B
1 kg
E
5m
1m
5m
0.5 m
C
0.5 m
Greatest
15 kg
5 kg
F
10 m
7.5 m
0.75 m
1 _______ 2 _______ 3 _______ 4 _______ 5 _______ 6 _______
Least
Or, all masses will have the same kinetic energies. _________
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
64
7
8
Very Sure
9
10
P. Marquard, D. Maloney
Physics Ranking Tasks
68
Mechanics
Ball Motion Diagram—Kinetic Energy 67
The following drawings indicate the motion of a ball subject to one or more forces on various surfaces
from left to right. Each circle represents the position of the ball at succeeding instants of time. Each timeinterval between positions is equal. In all situations, the balls start with the same velocity.
Rank each case from the highest to the lowest final kinetic energy based on the figures using the
coordinate system shown in the diagram. Assume the acceleration for each situation to be constant.
A
D
B
C
E
F
Highest 1________ 2________ 3________ 4________ 5________ 6________ Lowest
Or, all have the same final kinetic energy._________
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
67
7
8
Very Sure
9
10
D. Maloney
Physics Ranking Tasks
71
Mechanics
Equal Forces on Boxes—Work Done on Box 68
In the figures below, identical boxes of mass 10 kg are moving at the same initial velocity to the right on
a flat surface. The same magnitude force, F, is applied to each box for the distance, d, indicated in the
figures.
Rank these situations in order of the work done on the box by F while the box moves the indicated
distance to the right.
A
B
C
F
F
F
d=5m
d = 10 m
d=5m
F
F
D
E
F
F
d = 10 m
d=5m
d=5m
Greatest 1_______ 2________ 3________ 4________ 5________ 6________ Least
Or, all of the boxes experience the same work. _______
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
68
7
8
Very Sure
9
10
E. Eckard
Physics Ranking Tasks
72
Mechanics
Velocity Time Graph—Work Done on Box 70
Shown below is a graph of velocity versus time for an object that moves along a straight, horizontal line
under the, perhaps intermittent, action of a single force exerted by an external agent.
Rank the intervals shown on the graph, from greatest to least, on the basis of the work done on the object
by the external agent.
(m/s)
8
V
6
B
e
4
C
A
l
D
2
G
Time (s)
o
5
c
10
15
-2
20
E
25
30
35
F
i
-4
t
-6
y
-8
Greatest 1_______ 2_______ 3_______ 4_______ 5_______ 6______ 7
Least
Or, the agent does the same amount of work during all of these intervals. _________
Or, the agent does not work during any of these intervals.
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
70
7
8
Very Sure
9
10
C. Hieggelke, D. Maloney, T. O’Kuma
Physics Ranking Tasks
74
Mechanics
Pendulums—Maximum Speed of the Bob71
Shown below are six situations where spheres are attached to strings forming pendulums. The pendulums
vary in mass and length, but the angles from the vertical are the same for all.
Rank these situations, from greatest to least, on the basis of the maximum speed of the bob at the bottom
of the swing. In other words, put first the pendulum whose bob has the greatest speed going through the
equilibrium point and put last the pendulum whose bob has the least speed at equilibrium.
A
B
C
3m
5m
4m
0.600 kg
0.750 kg
0.400 kg
D
E
F
4m
3.5 m
3m
0.750 kg
0.400 kg
0.500 kg
Greatest 1________ 2________ 3________ 4________ 5________ 6_______ Least
Or, the maximum speed is the same for all six of these. __________
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
7
8
71
Very Sure
9
10
C. Hieggelke, D. Maloney, T. O’Kuma
Physics Ranking Tasks
75
Mechanics
Force Pushing Box—Change in Kinetic Energy 72
Various similar boxes are being pushed for 10 m across a floor by a net horizontal force as shown below.
The mass of the boxes and the net horizontal force for each case are given in the indicated figures.
Rank the change in kinetic energy for each box from the greatest change in kinetic energy to the least
change in kinetic energy. All boxes have an initial velocity of +10 m/s ( + direction is to the right and to the left with –4 < -2).
10 kg
F = 100 N
15 kg
F = 50 N
A
20 kg
F = 75 N
B
20 kg
F = 50 N
C
10 kg
F = 75 N
D
15 kg
F = 100 N
E
10 kg
F = 50 N
G
F
20 kg
F = 100 N
H
Greatest 1 _____ 2 _____ 3 _____ 4 _____ 5 _____ 6 _____ 7 _____ 8 _____ Least
Or, all changes in kinetic energy are the same.
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
72
7
8
Very Sure
9
10
T. O’Kuma
Physics Ranking Tasks
76
Mechanics
Pushing Box with Friction—Change in Kinetic Energy 73
Various similar boxes are being pushed for 10 m across a floor by a horizontal force as shown below. The
weights of the boxes and the applied horizontal force for each case are given in the indicated figures. The
frictional force is 20% of the weight of the box (g = 10 N/kg).
Rank the change in kinetic energy for each box from the greatest change in kinetic energy to the least
change in kinetic energy. All boxes have an initial velocity of +10 m/s ( + direction is to the right and - to
the left, with –4 < -2).
10 N
F = 100 N
10 N
F = 50 N
A
20 N
F = 100 N
B
20 N
F = 50 N
C
10 N
F = 10 N
D
20 N
F = 10 N
E
50 N
F = 10 N
G
F
100 N
F = 20 N
H
Greatest 1 _____ 2 _____ 3 _____ 4 _____ 5 _____ 6 _____ 7 _____ 8 _____ Least
Or, all changes in kinetic energy are the same.
Please carefully explain your reasoning.
How sure were you of your ranking? (circle one)
Basically Guessed
Sure
1
2
3
4
5
6
73
7
8
Very Sure
9
10
C. Hieggelke, T. O’Kuma
Physics Ranking Tasks
77
Mechanics