COVER PAGE
CHAPTER 7 EXAM (50 POINTS TOTAL)
Please do not begin this exam until instructed to do so. You may use a calculator and a pencil/pen for
the exam. Please be sure to write your name, date, and period on the first page, and write clearly and
legibly on the exam.
When you are finished, please bring your exam to me and begin working on the Chapter 8 Seatwork
on the side board.
GOOD LUCK!!
Name:_________________________________________ Date: _______________ Per:__________
CHAPTER 7 EXAM (50 PTS.)
Matching – Match the following statements with the best word from the box. Write the correct letter in the
blank provided. Words may be used more than once or not at all. (1 pt. each)
1. ____ Inertia in motion
2. ____ The force applied over a certain time interval
3. ____ The unit for momentum
4. ____ When objects collide without being permanently deformed
and without generating heat
5. ____ Speed in a given direction
6. ____ The unit for impulse
7. ____ When objects collide and tangle or stick together
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
Conserved
Impulse
Elastic collision
Inelastic collision
Momentum
Law of Conservation
of Momentum
Mass
Velocity
Newtons x seconds
Kg x m/s
8. ____ Without any external forces, momentum is never lost or
gained
9. ____ Term that applies to any physical quantity that remains unchanged during interactions.
10. ____ In order to have momentum, and object must have velocity and ____________.
True/False – Circle T if the statement is true or F if any of the statement if false. If a statement is
false, correct the statement to make it true. An example has been done for you (1.5 pts. each)
best
T F Mr. ------- is the worst teacher ever.
11.
T F An object that is not moving does not have momentum.
12.
T F A change in momentum is created by an impulse.
13.
T F 2 pool balls colliding is an example of an inelastic collision.
14.
T F Something that does not have mass cannot have momentum.
15.
T F When 2 train cars collide and connect together as they roll, this is an example of an inelastic
collision.
16.
T F Momentum is conserved in only elastic collisions, not inelastic ones.
17.
T F Impulses are less when objects bounce.
18.
T F If an object’s velocity is doubled, its momentum is decreased by half.
19.
T F Airbags in cars save lives by decreasing the impact time of our body on the car.
20.
T F If no net forces or impulses act on a system, the momentum of that system cannot change.
Short Answer - Answer the following questions in complete sentences. Be as clear and concise as
possible (2 pts each).
21. Why does an egg break when thrown against a brick wall, but not against a bed sheet? (hint – think
of impulse and how fast the egg slows down)
22. In our Explosion lab, how did the momentums compare between the more massive and less massive
cars when they were released? How is this possible if one car is much more massive than the other?
23. A roller skate and a large truck have the same momentum. Describe how this could be possible.
24. A rifle and a bullet are at rest before firing.
a. What is the net momentum of the rifle and the bullet before firing? Explain.
b. The bullet is then fired from the rifle. What is the net momentum now? Explain.
Word Problems – Solve the following problems. Please show all equations and work, and use the
correct units.
25. A 300 kg car travels at 11 m/s. What is its momentum? (2 pts.)
26. A 250 kg truck travels with a momentum of 560 kg x m/s. What is its velocity? (2 pts.)
27. A ball is pushed for 3 seconds with a force of 50 Newtons. What is the impulse on the ball? (2 pts.)
28. In an elastic collision, a 5 kg ball traveling at 5 m/s hits a 7 kg ball at rest. The 5 kg ball transfers all
its momentum over to the 7 kg ball.
a. What is the total momentum of the 2 balls before they collide? (1 pt.)
b. What is the total momentum of the 2 balls after they collide? (1 pt.)
c. What type of collision is this? (1 pt.)
d. At what velocity does the 7 kg ball move after the collision? (2 pts.)
29. Jocko the clown, whose mass is 60 kg, stands on a skateboard. A 20 kg ball is thrown at Jocko at
3 m/s, and when he catches the ball, he and the ball move on the skateboard.
a. What is the total momentum of Jocko and the ball before they collide? (1 pt.)
b. What is the total momentum of Jocko and the ball after they collide? (1 pt.)
c. What type of collision is this? (1 pt.)
d. How fast do Jocko and the ball move after he catches the ball? (2 pts.)
Answer Key:
Matching (1 pt. each):
1. E
2. B
3. J
4. C
5. H
6. I
7. D
8. F
9. A
10. G
True – False (1.5 pts. each, 1 pt for correct answer and 0.5 pts. for corrections):
11. True
12. True
13. False – 2 pool balls colliding is an example of an elastic collision.
14. True
15. True
16. False – Momentum is conserved in both types of collisions.
17. False – Impulses are greater when objects bounce.
18. False – If an object’s velocity is doubled, its momentum is doubled.
19. True
20. True
Short Answer (2 pts each):
21. The bed sheet increases the time that it takes for the egg to slow down, which creates less stress on
the egg and therefore does not crack the egg. When an egg is thrown against a brick wall, the time it
takes to slow down is very fast, thus creating more stress on the egg.
22. The momentums of both the more massive and less massive car were the same when they were
released. This is possible because although one car has more mass, it moves slower than the car with
less mass, making their momentums equal.
23. Since the roller skate has much less mass than the truck, it must be moving with much more velocity
than the truck in order to have the same momentum.
24. A – the net momentum of the bullet and rifle before firing are zero. Neither is moving.
B – The net momentum is still zero. After firing, the bullet moves fast but has little mass, while the
rifle moves slow in the opposite direction but has much more mass. Since they move in the opposite
directions, the net momentum of the system is zero.
Word Problems-Item points vary (Items 25-27 – 1 pt. for work and 1 pt. for correct answer, Items 28-29
point values vary by question):
25. 3300 kg x m/s
26. 2.24 m/s
27. 150 N x s
28. Points vary
a. 25 kg x m/s (1 pt.)
b. 25 kg x m/s (1 pt.)
c. Elastic collision (1 pt.)
d. 3.6 m/s (1 pt. for calculations and 1 pt. for correct answer)
29. Points vary
a. 60 kg x m/s (1 pt.)
b. 60 kg x m/s (1 pt.)
c. Inelastic collision (1 pt.)
d. 0.75 m/s (1 pt. for calculations and 1 pt. for correct answer)
Student Description:
This Conceptual Physics test was designed for students at the 9th grade level who are operating at the
Algebra I math level. The students have already spent the previous months learning about mass, velocity,
force, and time. These are the basic units that they need for this Chapter test, which deals with momentum,
impulse, and different types of collisions. Some students may also have lower than normal math levels, and
there are approximately 8 students who are either ELL students or students with special needs in the class.
CA State Standards:
The laws of conservation of energy and momentum provide a way to predict and describe the movement of
objects. As a basis for understanding this concept:
1. Students know how to calculate the momentum as the product mv.
2. Students know that momentum is a separately conserved quantity different from energy.
3. Students know an unbalanced force on an object produces a change in its momentum.
4. Students know how to solve problems involving elastic and inelastic collisions in one dimension by
using the principles of conservation of momentum and energy.
Learning Objectives (Numbers correspond to CA State Standards above). By the end of this unit, the
student will be able to:
1A – Calculate the momentum of an object using the product of the mass times its velocity, and use the
correct units of kg x m/s.
2A – Explain why in the absence of outside forces, momentum in a system is neither created nor destroyed.
3A – Describe the concept of impulse, and that impulses create a change in momentum of an object.
3B – Calculate the impulse on an object using the force on an object multiplied by the time of contact, and
use the correct units of N x s.
3C – Explain why impulses and the time it takes an object to decrease its momentum are important in
collisions, such as airbags in automobiles.
4A – Describe the differences between elastic and inelastic collisions.
4B – Solve problems involving elastic and inelastic collisions by using the principles of conservation of
momentum.
Table of Specifications
Item numbers for each standard/objective and type of question are specified, along with the points. Some
questions, such as word problems, cover multiple objectives and thus have partial points per objective.
Standard / Objective
1. Students know how to calculate the
momentum as the product mv.
1A – Calculate the momentum of an object using
the product of the mass times its velocity, and
use the correct units of kg x m/s.
16.5 points total
2. Students know that momentum is a separately
conserved quantity different from energy.
2A – Explain why in the absence of outside
forces, momentum in a system is neither created
nor destroyed.
11 points total
3. Students know an unbalanced force on an
object produces a change in its momentum.
3A – Describe the concept of impulse, and that
impulses create a change in momentum of an
object.
2.5 points total
3. Students know an unbalanced force on an
object produces a change in its momentum.
3B – Calculate the impulse on an object using
the force on an object multiplied by the time of
contact, and use the correct units of N x s.
3 points total
3. Students know an unbalanced force on an
object produces a change in its momentum.
3C – Explain why impulses and the time it takes
an object to decrease its momentum are
important in collisions, such as airbags in
automobiles.
5 points total
4. Students know how to solve problems
involving elastic and inelastic collisions in one
dimension by using the principles of
conservation of momentum and energy.
4A – Describe the differences between elastic
and inelastic collisions.
7 points total
4. Students know how to solve problems
involving elastic and inelastic collisions in one
dimension by using the principles of
conservation of momentum and energy.
Matching
True/False with
corrections
Short
Answer
Word Problems
1, 3, 5, 10 (1 pt.
each)
11, 14, 18 (1.5 pts.
each)
23 (2 pts.)
25, 26 (2 pts. each)
28a, 29 a (1 pt.
each)
4 pts. total
4.5 pts. total
8,9 (1 pt. each)
16, 20 (1.5 pts.
each)
22, 24 (2 pts.
total)
28b, 29b (1 pt.
each)
3 pts. total
4 pts. total
2 pts. total
n/a
n/a
2 pts. total
2 (1 pt. each)
12 (1.5 pts. each)
1 pt. total
1.5 pts. total
2 pts. total
6 pts. total
6 (1 pt. each)
27 (2 pts. each)
n/a
n/a
1 pt. total
n/a
4, 7 (1 pt. each)
2 pts. total
n/a
2 pts. total
17, 19 (1.5 pts.
each)
21 (2 pts.
each)
3 pts. total
2 pts. total
13, 15 (1.5 pts.
each)
n/a
3 pts. total
n/a
28c, 29c (1 pt.
each)
2 pts. total
n/a
4B – Solve problems involving elastic and
inelastic collisions by using the principles of
conservation of momentum.
4 points total
Problem type totals:
n/a
28d, 29d (2 pts.
each)
4 pts. total
10 points total
15 points total
8 points
total
16 points total
Explanations and Rationale/CIAS Links
This exam was intended for 9th grade level students with low math levels, typically Algebra I or
equivalent. Since physics classes commonly use very complex math, the Conceptual Physics course was
designed for students so that they could understand important concepts in physics without using any
complex math. My class contains mostly 9th grade students, with some 10th and 11th graders mixed in based
on their current math levels. For this exam, a student only needs to use only basic algebra to solve the word
problems, and most of the other exam questions deal with concepts rather than mathematics.
In terms of the numbers and types of questions used on this exam, I used 10 problems each of
matching and true/false, 4 short essays, and 5 word problems. The point distributions were somewhat even
between types of questions, with 10 points for matching, 15 points for true/false, 8 points for the short
essays, and 16 points for the word problems. Although the matching questions do not require much higherlevel thinking, I often include them on exams because it they are straightforward and easy to grade
(practicality and reliability), and they meet the need for some lower order questions for the exam. I feel that
it is good for students to begin the exam with some easier questions, in order to build up their confidence
and refresh their memories a bit. An exam which begins with very difficult, higher-level thinking questions
may frustrate students and ruin the rest of the exam for them. I also like to use true/false questions, but with
corrections on the false statements. Instead of the students just guessing the answer and having a 50%
chance of getting it correct, I require them to do a bit higher level of thinking and explain to me why a
statement is incorrect. The only problems I encounter with this type of question are that there can be a wide
range of changes made to the false statements that could be correct. This makes the problems more difficult
and more time consuming to grade. This could be a reliability issue, but I try and make the corrections to the
statements as obvious and straightforward as possible.
The short essay questions and word problems on the exam serve multiple uses. First of all, they force
students to show their understanding of concepts and learning objectives. Obviously, this is an important
part of assessing them – we want to know what they have learned and understand. I feel that short essay and
word problems give me a better idea of assessing what the students know. In a sense, I feel that these types
of questions are more valid than matching or multiple-choice questions, since a student may be good at
taking multiple choice exams but may not necessarily have a mastery of the content. Short essay and word
problems also force the students to think on a higher level, and to express themselves in their own words. If
we are going to assess for learning, we need to have the students think on a higher level and to organize
information independently. Also, as educators we are required to help the students read and write, so short
essay questions and word problems can help with this. Even if a student is an ELL student or does not write
well, I do not grade the answers based on grammar or sentence structure, only content. I do require them to
write in complete sentences and to explain their answers thoroughly.
In analyzing the numbers of points for each of the standards/objectives, I feel that my exam covers
all the 4 standards evenly and touches all of the objectives for the unit. I have 16.5 points allotted for
standard 1, 11 points for standard 2, 10.5 points for standard 3, and 11 points for standard 4. The exam
mirrors my depth and breadth of instruction, since I spent more time covering momentum and how to
calculate momentum (Objective 1), and less time covering impulse (Objective 3a) in class. Since I feel that
word problems are so important in physics, I did tend to cover these types of questions more in-depth in my
instruction and on the exam. For word problems #28 and 29, I scaffolded the questions into multiple parts to
include different learning objectives into each question. Instead of just having the students solve for the final
answer, I asked them guiding questions that hopefully led them to the correct final answer. For example, in
question # 28, I first ask the student to calculate the initial momentum before collision (Objective 1A), then
I ask them to figure out the final momentum after the collision (Objective 2A). I then ask them to identify
the type of collision (Objective 4A) and then finally to calculate the final velocity of the object using the
idea of conservation of momentum (Objective 4B). I could just ask them the final velocity of the object,
with the understanding that they must incorporate all these other concepts to find the final answer, but I feel
that guiding them through the process makes it easier for the student to find the final answer and helps them
understand how the concepts interrelate to each other.
RSVP Issues
Reliability – In terms of reliability, I feel that my exam avoids most reliability issues. Since the students
write their answers directly on the exam, there is no chance of information being lost due to transfer to a
separate answer document. In addition, the directions for each task are clearly stated, along with the point
values for each question. There is plenty of space for the student responses, and all the questions have
straightforward, clear answers.
Standardization – The same exam was given to each student, although I typically use different versions of
the same exam for each class. The versions are the exact same questions, but just in a different order. In
order to be fair for all students, I address all questions that students have to the whole class, so that I don’t
unfairly help one student and not others while answering clarifying questions. The exam is meant to be
finished in 20-30 minutes, but the students have 56 minutes to finish the exam. If they finish early, they
have something to work on quietly while the other students finish. This gives all students adequate time to
finish the exam.
Validity – As you can see from the Table of Specifications, the exam questions are directly aligned with the
content standards and the learning objectives for the chapter. I designed the test to align directly with the
instruction and content taught during class, and I varied the amounts of each question to reflect the depth of
instruction during class. The word problems from the exam were very similar to the ones we reviewed and
practiced in class, and so a student who listened in class, did all the class work and homework, and studied
for the exam should do very well on this exam. In addition, the CIAS links should be sound, since the test is
valid and is based directly off the standards, objectives, and instruction during class.
Practicality – The exam overall is not difficult to grade, especially the matching and true/false portions.
Although the short essay and word problem portions may take a little more time to grade, the difficulty of
grading is low and I would be able to return the exam to the students in a reasonable amount of time.
Next Steps for Teaching
In terms of providing feedback to the students and determining the next steps for teaching, the first
step would be to review the exam when returning it to the students. Although it is difficult to explain all the
small mistakes in my feedback to the students, I can make these explanations to the whole class and address
student concerns at the same time. One area where I anticipate concerns for the students is the word
problems. If I find that many students performed poorly on the word problem portion of the exam, I have
some different options. One concept that I have been using lately with good results is beginning the class
with a “warm up” word problem. The students have a few minutes to work on the problem individually, and
then they have a few minutes to compare answers with a partner before handing in their work. This seems to
clarify situation for many of the students. I have also tried giving the students a general outline that they can
use on every word problem. The outline gives the students steps to follow and important questions to answer
as they move through the word problem. It is a form of scaffolding that seems to have good results.
In addition, I anticipate the students will have problems on conservation of momentum in elastic and
inelastic collisions. I have seen some great video demonstrations on these types of collisions, where they
show the demonstration and explain how things are happening. Maybe I can have the students work in
groups to design their own demonstration, using common objects they have at home or school. One group
will give a demonstration on elastic collisions, while another will demonstrate inelastic collisions.