PREPARING FOR THE AP PHYSICS EXAM Presented by: DOLORES GENDE

PREPARING FOR THE

AP PHYSICS EXAM

Presented by:

DOLORES GENDE

PREPARING FOR THE AP PHYSICS EXAM

TOPICS

I. Understanding the AP Physics ExamMultiple-Choice SectionFree-Response Section

II. Exam Preparation Resources

III. Exam Taking Strategies

AP PHYSICS EXAM 2009 AP Physics B 70 multiple-choice questions (90 pts)2 long free-response questions (15 pts each)5 short free-response questions (10 pts each)___________________________________________________

180 minutes 170 total points (Scaled to 180)

I. UNDERSTANDING THE AP EXAM

Section I: Multiple-Choice QuestionsThis section emphasizes the breadth of the students’ knowledge and their understanding of the basic principles of Physics.

The AP Physics Exam contains the following types of multiple-choice questions:

Conceptual Questions Computation Questions Variable-Manipulation Questions Graphical Analysis Questions Diagram-Based Questions Other Types of Questions

Section I: Multiple-Choice Questions

Conceptual Questions:

These type of questions are theoretical in nature and do not require a mathematical solution.

Understanding the principles underlying physics concepts is very important as well as knowledge of the relationships among variables.

B1. A solid metal ball and a hollow plastic ball of the same external radius are released from rest in a largevacuum chamber. When each has fallen 1m, they bothhave the same:

(A) inertia (B) speed (C) momentum (D) kinetic energy (E) change in potential energy

Answer: B

Speed: both fall at the rate v = gt

B55. In an experiment, light of a particular wavelength isincident on a metal surface, and electrons are emitted from the surface as a result. To produce more electronsper unit time but with less kinetic energy per electron, the experimenter should do which of the following?

(A) Increase the intensity and decrease the wavelength of the light.(B) Increase the intensity and the wavelength of the light.(C) Decrease the intensity and the wavelength of the light.(D) Decrease the intensity and increase the wavelength of the light.(E) None of the above would produce the desired result.

Answer: BIncreasing the intensity and the wavelength.Increasing the wavelength decreases the frequency (inversely proportional) and decreases the energy since E α f

B64. Two parallel conducting plates, separated by a distance d, are connected to a battery of emf . Which of the following is correct if the plate separation is doubled while the battery remains connected?

(A) The electric charge on the plates is doubled. (B) The electric charge on the plates is halved. (C) The potential difference between the plates is doubled. (D) The potential difference between the plates is halved (E) The capacitance is unchanged.

Answer: B 1

2o

AC

d d C

Q

V

Sometimes multiple-choice questions will ask the student to identify the correct item or items from a list labeled with Roman numerals.

B5. Units of power include which of the following?I. Watt II. Joule per second III. Kilowatt‑hour

(A)I only (B) III only (C) I and II only

(D) II and III only (E) I, II, and III

Answer: C

JW

s

B7. Three forces act on an object. If the object is intranslational equilibrium, which of the following must be true?

I. The vector sum of the three forces must equal zero.II. The magnitudes of the three forces must be equal.III. All three forces must be parallel.

(A) I only (B) II only (C) I and III only (D) II and III only (E) I, II, and III

Answer: A

0F

B11. Which of the following experiments provided evidencethat electrons exhibit wave properties?

I. Millikan oil‑drop experimentII. Davisson‑Germer electron‑diffraction experimentIII. J. J. Thomson's measurement of the charge to‑mass ratio of electrons

(A) I only (B) II only (C) I and III only

(D) II and III only (E) I, II, and III

Answer: B

Diffraction is a wave property only.

Sometimes multiple-choice questions will ask the student to select items from two or three columns.

B27. When light passes from air into water, the frequency of the light remains the same. What happens to the speedand the wavelength of light as it crosses the boundary in going from air into water?

Speed Wavelength(A) Increases Remains the same(B) Remains the same Decreases (C) Remains the same Remains the same(D) Decreases Increases(E) Decreases Decreases

Answer: EBoundary behavior: speed decreasesand wavelength decreases (v = fλ)

C2. The velocity of a projectile at launch has a horizontal component vh and a vertical component vv. Air resistance is

negligible. When the projectile is at the highest point of its trajectory, which of the following show the vertical and horizontal components of its velocity and the vertical component of its acceleration?

Vertical Velocity Horizontal Velocity Vertical Acceleration

(A) vv vh 0

(B) vv 0 0

(C) 0 vh 0

(D) 0 0 g (E) 0 vh g

Answer: EProjectile motion


Computation Questions

These questions require basic application of physical concepts through mathematical computation. There is a need to recall the equation that governs the relationships between the given quantities, and finally, to perform the required computation and produce an exact numerical answer.

B2. A student weighing 700 N climbs at constant speed to the top of an 8 m vertical rope in 10 s. The average powerexpended by the student to overcome gravity is most nearly

(A) 1.1 W (B) 87.5 W (C) 560 W (D) 875 W (E) 5,600 W

Answer: C

700(8)560 W

10

W mghP

t t

B70. A 4 F capacitor is charged to a potential difference of 100 V. The electrical energy stored in the capacitor is

(A) 2 x 10-10 J (B) 2 x 10‑8 J (C) 2 x 10‑6 J (D) 2 x 10-4 J (E) 2 x 10-2 J

Answer: E

2 6 21 1(4 10 )(100)

2 2PE CV x

6 4 21(4 10 )(1 10 ) 2 10 J

2x x x

Sometimes multiple-choice questions will include solutions that should be calculated as estimations.

Questions 46-47A magnetic field of 0.1T forces a proton beam of 1.5 mA to move in a circle of radius 0.1 m. The plane of the circle is perpendicular to the magnetic field. B46.Of the following, which is the best estimate of the work done by the magnetic field on the protons during one complete orbit of the circle?

(A) 0 J (B) 10-22 J (C) 10-5 J (D) 102 J (E) 1020 J

Answer: ANo work is done, force acts perpendicular to displacement.

Questions 46-47A magnetic field of 0.1T forces a proton beam of 1.5 mA to move in a circle of radius 0.1 m. The plane of the circle is perpendicular to the magnetic field. B47. Of the following, which is the best estimate of the speed of a proton in the beam as it moves in the circle?

(A) 10-2 m/s (B) 103 m/s (C) 106 m/s (D) 108 m/s (E) 1015 m/s

Answer: C

2mvqvB

r

19 1 16

27

(10 )(10 )(10 )10

10

qBrv

m

Multi-Step Computation Questions

Sometimes the calculations may require more than one step to solve a problem.


B19. A rectangular wire loop is at rest in a uniform magnetic field B of magnitude 2 T that is directed out of the page. The loop measures 5 cm by 8 cm, and the plane of the loop is perpendicular to the field, as shown. The total magnetic flux through the loop is:

(A) zero (B) 2 x 10‑3 T‑m2 (C) 8 x 10‑3 T-m2 (D) 2 x 10‑1 T-m2 (E) 8 x 10-1 T-m

Answer: C BA

3 2(.004)(2) 8 10 Tmx

20.05 0.08 .004 mA

Variable-Manipulation Questions

These questions require variable manipulation using existing equations to form new relations. The answers will be in variable form.


B3. A railroad car of mass m is moving at speed v when it collides with a second railroad car of mass M which is at rest. The two cars lock together instantaneously and move along the track. What is the speed of the cars immediately after the collision?

(A) v/2 (B) mv /M (C) Mv /m (D) (m + M )v/m (E) mv /(m+M)

( )mv m M V mv

Vm M

Answer: E

B9. A child pushes horizontally on a box of mass m which moves with constant speed v across a horizontal floor. The coefficient of friction between the box and the floor is . At what rate does the child do work on the box?

(A) mgv (B) mgv (C) v/ mg (D) mg/v (E) mv2

Answer: ARate = Power

fF F N mg

W Fx

P Fv mg vt t

B40. What is the kinetic energy of a satellite of mass m that orbits the Earth, of mass M, in a circular orbit of radius R?

(A) Zero (B) (C)

(D) (E)

1

2

GMm

R1

4

GMm

R

1

2 2

GMm

R

GMm

R 2

C gF F

Answer: BCentripetal force is provided by Gravitational force

2

2

mv mMG

R R

2 GMv

R

21 1

2 2

GMK mv m

R

Questions 59‑60A rock of mass m is thrown horizontally off a building from a height h, as shown. The speed of the rock as it leaves the thrower’s hand at the edge of the building is v0.

B59.How much time does it take the rock to travel from the edge of the building to the ground?

(A) (B) (C)

(D) (E)

hvoh

v0

hv

g0

2h

g2h g

Answer: EProjectile motion

21

2y gt

2ht

g

Questions 59‑60A rock of mass m is thrown horizontally off a building from a height h, as shown. The speed of the rock as it leaves the thrower’s hand at the edge of the building is v0.

B60. What is the kinetic energy of the rock just before it hits the ground?

(A) mgh (B) ½ mv02 (C) ½ mv0

2 – mgh

(D) ½ mv0

2 + mgh (E) mgh - ½ mv02

Answer: DConservation of Energy

f o oK K U 21

2 omv mgh

Questions 21‑22A block of mass m is accelerated across a rough surface by a force of magnitude F that is exerted at an angle with the horizontal, as shown. The frictional force on the block exerted by the surface has magnitude f.

C21. What is the acceleration of the block? (A) F/m (B) F cos / m (C) (F-f ) /m (D) (F cos -f ) /m (E) (F sin -mg) /m

Answer: DFBD

f

Fg

NF

cosxF F f ma

cosF fa

m

Questions 21‑22A block of mass m is accelerated across a rough surface by a force of magnitude F that is exerted at an angle with the horizontal, as shown. The frictional force on the block exerted by the surface has magnitude f.

Answer: E

f

Fg

NF

C22. What is the coefficient of friction between the block and the surface?

(A) f /mg (B) mg / f (C) (mg -Fcos) / f

(D) f / (mg -Fcos) (E) f / (mg -Fsin)

sin 0y gF N F F

( sin )gf N F F

sin

f

mg F

Graphical-Analysis Questions

Some multiple-choice questions include a graph that must be interpreted in order to obtain the answer.


B8.The graph represents the potential energy U as a function of displacement x for an object on the end of a spring oscillating in simple harmonic motion with amplitude x0. Which of the following

graphs represents the kinetic energy K of the object as a function of displacement x ?

Answer: DConservation of Energy U = K

Questions 43‑44Three objects can only move along a straight, level path. The graphs below show the position d of each of the objects plotted as a function of time t.

B43. The magnitude of the momentum of the object isincreasing in which of the cases?

(A)II only (B) III only (C) I and II only

(D) I and III only (E) I, II, and III

Answer: BIncreasing momentum: accelerationGraph I: constant speed, Graph II: at rest

Questions 43‑44Three objects can only move along a straight, level path. The graphs below show the position d of each of the objects plotted as a function of time t.

B44. The sum of the forces on the object is zero in which of the cases?(A) II only (B) III only (C) I and II only (D) I and III only (E) I, II, and III

Answer: CNet force is zero for objects at rest or at constant velocity

C3. The graph shows the velocity v as a function of time t for an object moving in a straight line. Which of the following graphs shows the corresponding displacement x as a function of time t for the same time interval?

Answer: DGraph shows positive acceleration, constant velocity, negative acceleration.

(A) 40 kg m/s (B) 20 kg m/s (C) 0 kg m/s (D) ‑20 kg m/s (E) indeterminable unless the mass M of the object is known

C12. The graph shows the force on an object of mass M as a function of time. For the time interval 0 to 4 s, the total change in the momentum of the object is

Answer: CFt = m ΔvImpulse (Ft) = area under graphFt = 20 - 20 = 0 kg.m/s

Diagram-Based Questions

These questions require the interpretation of diagrams or the use of diagrams to obtain more information.


Questions 15‑16 refer to the diagram that shows part of a closed electrical circuit.

B15. The electrical resistance of the part of the circuit shown between point X and point Y is

(A) 4/3 (B) 2 (C) 2.75 (D) 4 (E) 6

Answer: ATwo resistors in series: 1+3 = 4

In parallel with the other:1 1 1

4 2ER

4(2) 8 4

4 2 6 3ER

Questions 15‑16 refer to the diagram that shows part of a closed electrical circuit.

B16. When there is a steady current in the circuit, the amount of charge passing a point per unit of time is (A) the same everywhere in the circuit(B) greater at point X than at point Y(C) greater in the 1 resistor than in the 2 resistor(D) greater in the 1 resistor than in the 3 resistor(E) greater in the 2 resistor than in the 3 resistor

Answer: ETotal current (V/RE) is divided between parallel branches of the circuit.

B51. Plane sound waves of wavelength 0.12 m are incident on two narrow slits in a box with nonreflecting walls, as shown. At a distance of 5.0 m from the center of the slits, a first‑order maximum occurs at point P, which is 3.0 m from the central maximum. The distance between the slits is most nearly

(A) 0.07 m (B) 0.09 m (C) 0.16 m (D) 0.20 m (E) 0.24 m

m Lx

d

1(0.12)(5)

0.2 m3

Answer: D

m Ld

x

Questions 39‑40As shown, two particles, each of charge +Q, are fixed at opposite corners of a square that lies in the plane of the page. A positive test charge +q is placed at a third corner.

C39. What is the direction of the force on the test charge due to the two other charges?

(A) (B) (C) (D)

(E)

Answer: E

Questions 39‑40As shown, two particles, each of charge +Q, are fixed at opposite corners of a square that lies in the plane of the page. A positive test charge +q is placed at a third corner.

C40. If F is the magnitude of the force on the test charge due to only one of the other charges, what is the magnitude of the net force acting on the test charge due to both of these charges?

(A) Zero (B) (C) F

(D) (E) 2

2

F

F2

Answer: DResultant force: 2 2 22 2F F F F

“Reverse” Multiple-Choice Questions

A variation of the standard multiple-choice question asks the student to choose which of five choices is incorrect. Set off by the words NOT or EXCEPT in capital letters, these questions are easy to identify.


B35. Quantum concepts are critical in explaining all of the following EXCEPT:

(A)Rutherford's scattering experiments (B)Bohr's theory of the hydrogen atom

(C) Compton scattering (D) the blackbody spectrum (E) the photoelectric effect

Answer: ARutherford experiment lead to the discovery of the atomic nucleus

x x x x x x x x x x x x x x x x

B

spring

B45. A metal spring has its ends attached so that if forms a circle. It is placed in a uniform magnetic field, as shown above. Which of the following will NOT cause a current to be induced in the spring?

(A) Changing the magnitude of the magnetic field(B) Increasing the diameter of the circle by stretching the spring(C) Rotating the spring about a diameter(D) Moving the spring parallel to the magnetic field(E) Moving the spring in and out of the magnetic field

Answer: DParallel will yield no current.

Section II: Free-Response QuestionsThis section emphasizes the application of basic principles of Physics in greater depth in solving more extended problems.

There is no generalized form for the free-response question, and there is no good way to categorize different “types” of questions. However, most of the free-response questions fall into three general groups as follows:

Computational QuestionsDerivation QuestionsLab-Based Questions

Section II: Free-Response Questions

Computational QuestionsInvolve solving a problem to produce a numerical answer.

Partial credit is awarded if part of the answer is correct. Often, answers to one part of a question must be used to solve the next part of the question. Exam readers take this into account, but the student must show all of the steps to receive credit. If they make a mathematical error in the first part of a question, it may make getting a numerically accurate answer for the other parts impossible. By showing their equations and reasoning, the students can be awarded points for those subsequent parts.

Merely writing relevant equations is insufficient for credit, since the tables of equations are provided.

B2. A wall has a negative charge distribution producing a uniform horizontal electric field. A small plastic ball of mass 0.01 kg, carrying a charge of ‑80.0 C is suspended by an uncharged, non-conducting thread 0.30 m long. The thread is attached to the wall and the ball hangs in equilibrium, as shown above, in the electric and gravitational fields. The electric force on the ball has a magnitude of 0.032 N.

a. On the diagram, draw and label the forces acting on the ball.

b. Calculate the magnitude of the electric field at the ball's location due to the charged wall, and state its direction relative to the coordinate axes shown.

c. Determine the perpendicular distance from the wall to the center of the ball.

d. The string is now cut.

i. Calculate the magnitude of the resulting acceleration ofthe ball, and state its direction relative to the coordinateaxes shown.

ii. Describe the resulting path of the ball.


Derivation Questions

Involve solving a problem by manipulating variables to give the answer in an equation form.

These questions often indicate which variables should be included in the final answer.

Again, it is important that every step is clearly shown.

B1. Two small blocks, each of mass m, are connected by a string of constant length 4h and negligible mass. Block A is placed on a smooth tabletop and block B hangs over the edge of the table.

Express all algebraic answers in terms of h, m, and g.

a. Determine the acceleration of block A as it descends.

b. Block B strikes the floor and does not bounce. Determine the time t = t1 at which block B strikes the floor.

c. Describe the motion of block A from time t = 0 to the time when block B strikes the floor.

d. Describe the motion of block A from the time block B strikes the floor to the time block A leaves the table.

e. Determine the distance between the landing points of the two blocks.


Lab-Based Questions

These questions may ask students to design an experiment, analyze data, identify sources of error and/or draw conclusions and suggest ways to improve experiments.

The best way to prepare the students for this type of questions is to conduct meaningful laboratory work throughout the course.

B4. In the circuit shown, A, B, C,and D are identical lightbulbs. Assume that the battery maintains a constant potential difference between its terminals (i.e., the internal resistance of the battery is assumed to be negligible) and the resistance of each lightbulb remains constant.

a. Draw a diagram of the circuit in the box below, using the following symbols to represent the components in your diagram. Label the resistors A, B. C, and D to refer to the corresponding light bulbs.

b. List the bulbs in order of their brightness, from brightest to least bright. If any two or more bulbs have the same brightness, state which ones. Justify your answer.

c. Bulb D is then removed from its socket.

i. Describe the change in the brightness, if any, of bulb A when bulb D is removed from its socket. Justify your

answer.

ii. Describe the change in the brightness, if any, of bulb B when bulb D is removed from its socket. Justify your

answer.

Special attention should be paid to directive words and phrases when reading the questions and only provide the information required by these terms:

"Justify" and "explain" call for an answer supported by prose, equations, calculations, diagrams, or graphs. The prose or equations may refer to fundamental ideas or relations in physics, such as Newton's laws, conservation of energy, Gauss' law, or Bernoulli's equation. In other cases, the justification or explanation may take the form of analyzing the behavior of an equation for large or small values of a variable in the equation.


"Calculate" means that students are expected to show work leading to a final answer, which may be algebraic, but which is more often numerical.

"What is" and "determine" indicate that students do not need to show their work to obtain full credit. But, showing work leading to answers is a good idea because partial credit can be earned in the case of an incorrect answer.

"Derive" is more specific and indicates that students need to begin their solution with one or more fundamental equations, such as those given on the AP Physics Exam equation sheet. The final answer, usually algebraic, is then obtained through the appropriate use of mathematics.


Other ResourcesMy website contains links to:

Preparing for the Exam AP Physics Review SessionsExam Preparation Strategies

Physics Conceptual FactsA list of +100 facts important Physics Concepts that the students need to know.

Open-Ended LabsFree-response lab ideas compiled by Hugh Henderson.

II. Exam Preparation Resources

http://apphysicsb.homestead.com/review.html

http://apphysicsb.homestead.com/physicsfacts.html

http://apphysicsb.homestead.com/labsoe.html

Advice for test-takers (Multiple Choice section)

Have a routine for taking MC tests.

Watch out for guessing.

Buy a good eraser.

Budget your time, and answer stuff you know first.

Don’t be fooled: you have to know the equations.

Read each question carefully.

Advice for test-takers (Free Response section)

Write legibly. If we can’t read it, we can’t grade it.

For symbolic answers, use the symbols given, not your own.

Budget your time, read all the questions first and answer stuff you know first.

Be familiar with what is and what isn’t on the equation sheet.

Answer the question that is asked.

Show all of your work, even if it’s obvious.


If you scratch out your work or erase it, it will not be examined.

On the other hand, putting down a wrong answer together with a correct answer most likely will negate the correct answer.

If you’re not sure of part (a) but you need it to answer part (b), make up something and follow through with the substitution.

Don’t forget units on your answers.

When asked to justify or explain, write in complete sentences.


Don’t assume the grader knows what you’re talking about. Leave nothing to the imagination.

Even if you’re not sure how to do a problem, write down what you can in words (if it’s relevant). You might get a few points, but leaving it blank won’t get you anything.

Put your answer in the space provided. If you need more space, clearly indicate where the extra work is.

It bears repeating: No Immaculate Answers.

SHOW

YOUR

WORK

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PREPARING FOR THE AP PHYSICS EXAM Presented by: DOLORES GENDE