January 2008 Regents Physics Exam Explained Chloe Miller
Part A – Question 1
For this question, you are looking for the answer that would have both a magnitude and a direction. A vector is a quantity that has both a magnitude (a numerical value) AND a direction (north, east, etc. ). On the other hand, a scalar is a quantity that only has a magnitude. The correct answer is Choice 4, displacement. Displacement is an object’s overall net change in position. It is a vector quantity because it includes how far away the object is from its original position and in what direction the object has moved. Take this example: You travel 3 meters north, then 4 meters east. Although you traveled 7 meters total (your distance traveled), your overall displacement is 5 meters northeast.
• Choice 1 is incorrect because speed is a scalar quantity. It only refers to how fast something is moving, and it does not tell you anything about what direction the object is moving. For example, a car can have a speed of 5 meters/second. • If you knew both how fast the object is moving and what direction it was moving in, then you would know its velocity vector, but that is not an answer here. For example, that same car may have a velocity of 5 meters/second north. • Choice 2 is incorrect because work is a scalar quantity. It is the product of force and displacement. Work is a measure of energy, and it does not have a direction. Therefore, it is not a vector quantity. • Choice 3 is incorrect because mass is a scalar quantity. It is the amount of matter that an object is made up of. There is no direction to it, so it is not a vector quantity.
Question 2
What we know: What we are looking for: Find the equation that includes all the variables that were given to you: Solve:
Question 3
Question 4
This is a trig question. Since you know the hypotenuse and you are looking for the adjacent side, you want to use cosine (cos). Refer back to SOH CAH TOA if you need to. Remember: If you’re using your calculator for trig problems, make sure your calculator is in the right mode (for this, it would need to be in degree (DEG) mode).
Question 5
Inertia refers to an object’s resistance to a change in its velocity. The more mass the object has, the greater its inertia. Therefore, for this question, you want to look for the object that has the greatest mass. Your answer is Choice 4 because its mass is greater than the others’.
Question 6
Question 7
This is one of those questions where something is launched off a cliff and it falls to the ground. For these questions, the only thing that affects the time it takes for the object to hit the ground is height (the vertical distance). However, due to the different horizontal speeds, the horizontal distances that the two spheres travel are different. Since the time is the same for both spheres, time is a constant for this. The only thing that affects the horizontal distance now is the horizontal speed of the spheres. Since is a constant (9. 81 m/s^2), the only actual variable that would determine what the time is is. Since Spheres A and B are launched from the same height, their times are the same and they will hit the ground at the same time. Since Sphere A has twice the speed of Sphere B, Sphere A will travel twice the distance horizontally. Therefore, Choice 2 is the answer.
Question 8
First, find the resultant force of the two given forces. In order to achieve equilibrium, the net force of the object has to be 0. The “additional force” that you are looking for needs to balance out the resultant force that you just found. In order to equal out the resultant force, the additional force needs to have the same magnitude but be in the opposite direction. Therefore, the additional force needs to be 28 N southwest, which is Choice 4.
Question 9
According to the equation for friction (found in your Reference Table), as the friction coefficient increases, the force of friction also increases. Therefore, in order to find the greatest force of friction, you need to find the material with the greatest friction coefficient. Refer to your Reference Table for this. According to the table, rubber has the greatest friction coefficient on dry concrete out of the four choices. Choice 1 is the answer.
Question 10
This is a question about circular motion. If an object is experiencing a centripetal force, the direction of the centripetal acceleration will always point toward the center of the circle. On the other hand, the velocity of the object will point in the direction tangent to the curve (the tangent line forms a right angle with the radius of the circle). Therefore, Choice 3 is correct.
Question 11
Question 12
This question is testing your knowledge of Newton’s Third Law of Motion. According to this law, for every action/force there is an equal and opposite reaction. In the context of this question, when the astronaut exerts the 50 N force on the satellite, the satellite must exert an equal and opposite force back on the astronaut. Therefore, the magnitude of the force by the satellite on the astronaut must also be 50 N, choice 4.
Question 13
This question is about the Law of Conservation of Momentum, which states that the total momentum of a closed system (“closed” means that no outside force is applied) is conserved. In terms of collisions, like in this question, this law means that the total momentum before the collision and the total momentum after the collision are the same. The total momentum of the system was “conserved. ” Therefore, Choice 3 is the answer.
Question 14
Student A Student B Both Student A and Student B do 20 J of work. However, Student B develops more power because they did the same amount of work in less time. Therefore, Choice 1 is the answer.
Question 15
Question 16
Since the stone is not moving at its maximum height in the air, all of the work done on the slingshot is converted into the potential energy of the stone at its maximum height.
Question 17
Question 18
This equation was given by Mr. Randall. It is not found in the Reference Table in this exact form. is 0 because the block ends up at the bottom of the incline with a height of 0. is 0 because the block starts at rest and the initial velocity is 0.
Question 19
Since there is 1 electron, the charge (q) equals 1 elementary charge (e), which then equals 1. 6 x 10^-19 C.
Question 20
Question 21
This question is about Ohm’s Law. If there is a constant potential difference (V stays constant), as resistance increases, current decreases. Likewise, as current increases, resistance decreases. Therefore, Choice 1 is correct. It is the only graph that shows a negative slope, or an inversely proportional relationship.
Question 22
Question 23
The amplitude of a sound wave affects how loud the sound is. It is a direct relationship, so if you increase the amplitude, you increase the loudness of the sound. Therefore, Choice 4 is the answer. FYI, the frequency of a sound wave affects the pitch of the sound. Review: The amplitude of a wave refers to the maximum height a particle moves from its rest/equilibrium position. Review: The frequency of a wave refers to how many cycles of the wave occur within a set period of time. Most times, the unit is in Hertz (Hz), which would refer to how many cycles occur per second.
Question 24
The period and frequency of a wave are inverses/reciprocals of each other, meaning that if you flip the equation for the period, you will get the frequency and vice versa. Since they are inverses, when you multiply them together, you get 1. Choice 1 is the answer.
Question 25
Question 26
Since it is an electromagnetic wave in a vacuum, the velocity is equal to c, the speed of light in a vacuum.
Question 27
Question 28
Question 29
Resonance occurs when one object vibrating at the same natural frequency of a second object causes that second object to vibrate. An example of resonance would be when you pluck a string on a guitar and produce notes. In order to have resonance, you would want the frequencies of the objects to be close. Therefore, Choice 1 is the answer.
Question 30
Charge is quantized, meaning that it can only come in whole-number increments of 1. 6 x 10^-19 C. For this question, you are looking for the answer that produces a whole number after you divide the charge by 1. 6 x 10^-19 C. Choice 3 is the answer.
Question 31
The “superposition” of the two pulses is when the two pulses “combine” for a brief moment. Since both of the pulses are cresting upward and are in the same pointed triangular shape, the superposition will also be pointed upward in the triangular shape, but it will be taller. Choice 3 is the answer.
Question 32
This is a question about the Doppler effect. According to the Doppler effect, the perceived frequency of a wave by an observer will change when there is relative motion between the observer and the source of the wave. When distance between the observer and the wave source increases (they get farther away from each other), the perceived frequency of the wave decreases. On the other hand, if the distance between the observer and wave source decreases, the perceived frequency of the wave increases. For this question, since the police car is approaching the pedestrian, the perceived frequency must be greater than the actual frequency of the siren. The only answer that is greater than 1. 00 x 10^3 Hz is 1. 10 x 10^3 Hz, Choice 4.
Question 33
As frequency increases, the energy of the photon also increases because h is a constant (Planck’s constant) Wavelength and frequency are inversely proportional with each other. As frequency increases, wavelength decreases. Since energy increases and wavelength decreases as frequency increases, Choice 3 is the answer.
Question 34
This question is about diffraction. When waves encounter obstacles and pass through small openings, they often bend and spread out. As a result, they will form curved, spherical waves, as seen in the picture to the left. Small obstacles and long wavelengths will produce maximum diffraction. Choice 4 is the answer.
Question 35
It is important to read the explanation of the diagram at the beginning. It describes how an electron and positron become energy, and the energy eventually produces the mesons. Even if you don’t know what the specific quarks are, you can figure out this problem as long as you read the explanation and known that electrons, positrons, and mesons are matter. The answer that describes the transition of matter to energy to matter again is Choice 2. To make sure the other choices are incorrect: • Choice 1: This is the reverse of what happens in the diagram. You do not start out with just energy, and the end result is matter. • Choice 3: The diagram starts out with an electron and positron, which are leptons, NOT baryons (see Reference Table for classification of matter) • Choice 4: The end results are mesons, which are NOT leptons.
Part B-1 – Question 36
If you don’t know the subunits of J and/or N off the top of your head, try to think of the units in terms of equations that use them. As with a lot of physics problems, there are many different ways to look at this question. This is just one of them.
Question 37
It can be difficult to think of weights in terms of newtons because we don’t use newtons often in daily life. It would help to put all of the answers in terms of pounds. 1 N =. 22 lb. An egg weighs about. 1 to. 2 pounds. To put this into perspective, a penny weighs about. 0055 pounds. You can then eliminate Choices 1 and 2 because an egg is not lighter than a penny. You can also eliminate Choice 4 because 22 pounds is about how much a car tire weighs. Choice 3 is the answer.
Question 38
In order to have the greatest resultant force, the two forces need to be acting on the object in the same direction. When the two forces are acting in the same direction, the angle between them is 0°. Choice 1 is the answer.
Question 39
Question 40
Gravitational forces only attract. On the other hand, electrostatic forces can either attract or repel. Opposite/unlike charges (+ and -) attract, and like charges (+ and +, or - and -) repel. The answer is Choice 1.
Question 41
As a spring is elongated from its equilibrium position (x), its potential energy (PE) increases exponentially. Choice 2 is the answer.
Question 42
Question 43
Question 44
This picture shows the electric field lines when the charges are positive and negative (left) and when the charges are both positive (right). For this question, both of the spheres are positive (like the right picture). Since they are both the same charge, the electric field lines at Point P are pointed upwards. Therefore, Choice 3 is the answer.
Question 45
In order to be unaffected by an electric field, the particle would have to be neutral/have a charge of 0 e, like a neutron. To find the charge, just add the 3 charges up, according to the info from the Reference Table. Choice 1 is the answer.
Question 46
Question 47
Question 48
This is about mass-energy equivalence. According to the equation, energy will increase in a direct proportion if the amount of mass increases. Therefore, the graph of mass vs. energy will be a straight line, Choice 1.
Question 49
Light is both reflected and refracted by glass. You need to look for the picture that shows both reflection and refraction. This is Choice 4. Reflection is when the wave hits the surface of the material and then bounces off in the opposite direction at the same angle. In the picture, the incident ray hits the glass from the left and then bounces off to the right at the same angle. Refraction is when a wave bends and changes speed when it enters a new medium/material. In the picture, the incident ray is refracted and bent so that it now points in a more downward direction. The reason why the ray was bent downward as opposed to the right (shown in Choice 1) is that crown glass has a higher absolute index of refraction than air (1. 52 vs. 1. 00). Remember, these values are found in the Reference Table.
Part B-2 – Question 50
When the spring is compressed, it has a certain amount of potential energy (PE). As the spring is released, all of that PE is converted into kinetic energy (KE). Therefore, set the equations for PE (of a spring) and KE equal to each other, and then solve for k.
Question 51
Always pay attention to the units! The information that they give you may not be in the units you are looking for, like with this. Make the necessary conversion from km to m. In general, don’t forget to show units with your answers for the short answer part of the exam!
Question 52
Notice how in the question, it says to “Show all work, including the equation and substitution with units. ” Make sure that when you substitute numbers into equations for the short answer questions, you don’t forget the units! FYI: In the scoring guide for the teachers who are grading the exams, this note was put for Question 52. A lot of questions will have a note like this, but not all of them do. It basically means that even if you don’t get the correct velocity for Question 51, you can still get credit for Question 52 as long as you correctly show the equation, substitution, and calculate the KE using the mass and whatever velocity you got for Question 51. Basically, don’t panic if you’re not sure your answer is right for a question with multiple parts. You still have the chance to get credit if you can use your answer correctly in later parts of the question.
Question 53
Long, hot, thin wires have a higher resistance. Short, cold, wide wires will have a lower resistance. When you stretch out the wire, it becomes longer and thinner. It becomes more difficult for electrons to flow along the wire, so the resistance increases. You can also look at the equation for resistance to see this. As the length of the wire (L) increases (since the wire becomes longer) and the cross-sectional area (A) decreases (since the wire becomes thinner), the resistance (R) increases as well.
Question 54
The resistivity (ρ) depends only on the material of the wire. Since the wire is the same material and stays at 20°C, the resistivity will stay constant/the same.
Question 55
Friction is what causes the car to slow down. As more work is done by friction, the speed of the car decreases, and the car has less kinetic energy. Therefore, as work done by friction increases, the kinetic energy decreases.
Question 56
First, figure out what you’re looking for. The angle of incidence for Mirror 2 is the angle created by the incident ray and the normal line. I drew in the normal line, which is perpendicular to the surface of Mirror 2. Then to actually find the angle of the incident ray, you can do it two ways. First, assuming you drew in the normal line correctly at 90° from Mirror 2, you should be able to use your protractor and measure the angle from the ray to the normal line. You should get 35°, with a margin of error of 2°.
*Honestly, if you don’t remember this from geometry and find this confusing, I’d recommend sticking with just using your protractor. Second, you can use geometry to reason it out. • The angle of incidence equals the angle of reflection for Mirror 1, so the angle of reflection (labeled “ 2”) must equal 55°. • Then, since the normal lines and the mirrors create a rectangle, the reflected ray of Mirror 1 (a. k. a. the incident ray for Mirror 2) acts as a diagonal for the rectangle. Therefore, since the alternate interior angles created by the diagonal of a rectangle are equal, Angle “ 3” equals Angle “ 2” and must be 55°. • Since the normal line is perpendicular to Mirror 2, the angle of incidence and Angle 3 must add up to 90° – 55° = 35°
Question 57
There are two ways you can draw the reflected ray. First, you could draw in the normal line for Mirror 2, and then measure 35° upward from the normal line and draw the reflected ray. Second, you could measure 55° to the left away from the surface of Mirror 2 and then draw the reflected ray.
Question 58
Since we are neglecting friction, the only force that the ball experiences at Point X is the force due to gravity. Therefore, the arrow you have to draw should point straight down toward the ground. There is no horizontal force since the ball is moving horizontally at a constant velocity, which means its horizontal acceleration is 0.
Question 59
This question is pretty much exactly the same as the previous question. Since there is no horizontal acceleration, the only acceleration that the ball experiences is the acceleration due to gravity. The arrow for Point Y should be pointing straight down toward the ground, just like the one for Point X.
Question 60
Question 61
Reminder: With equations like these, don’t forget to square things! It can be a common mistake to make. Reminder: Don’t forget units! Sometimes, the answer booklet (where you put your answers for the real exam) will put the units for you. For this question however, they did not put the units in the space for your work. You need to write them yourself.
Question 62
The Law of Conservation of Charge says that the net charge of an isolated system will always remain constant. For this question, this means that the charge of the stuff on the left side of the arrow must equal the charge of the stuff on the right side.
Part C - Questions 63 -66
63. ) Since the height goes from 0 to 25, there are enough lines on the x-axis for the scale to go up by 1 meter per line. The bolded lines mark every 5 meters. 64. ) Plot the points as accurately as you can. 65. ) When you draw a line or curve of best fit, try to draw it so that the points are equally distributed above and below your line. The line/curve does NOT have to hit the first and last points. Drawing a line or curve of best fit does NOT simply mean connecting all of the points either. It is possible that your line will just happen to go through every point, but don’t draw a crooked curve just so that it will connect all the dots. 66. ) According to my graph, the speed of the mass at 12. 5 m is about 15. 8 m/s. The scoring key allows for ±. 3 m/s of error. It also allows the grader to give you credit as long as your answer is consistent with your graph. So even if your graph somehow is incorrect, as long as your answer for Question 66 is right according to your graph, you can get credit.
Question 67
For this question, it probably would be quicker and easier to make a series circuit, not a parallel circuit. If each resistor is 5 ohms, then you would need 3 resistors to get to an equivalent resistance of 15 ohms. Make sure the resistors are all in a line, add a symbol for a source of potential difference (the one in the picture is a battery), and you should be done. Be sure that everything is connected, or else it won’t be a complete circuit.
Question 68
To have a smaller amplitude, the new wave must not go as high or as low as the original wave. To have the same wavelength, the distance between the crests (the high points) of the new wave must be the same as the original wave’s. • If you draw the new wave in phase with the original (meaning the waves have crests at the same time), then the new wave will kind of look like a flattened version of the old wave. • The new wave does NOT need to be in phase with the original, but it might simply be easier to draw them in phase with each other (as I drew to the left).
Question 69
As I mentioned in the previous question, if waves are in phase with each other, then they peak at the same time. This means that they are either 0° or 360° apart from each other. In terms of points on waves being in phase with each other, they need to be at the same position on the wave. For a point to be in phase with another point, it has to be in the same position/height but in a different section/cycle of the wave. All of the colored pairs of dots show examples of where points would be in phase with each other.
Question 70
To find what type of electromagnetic wave this wave is, look at its frequency. The explanation at the beginning of the question says it has a frequency of 6. 00 x 10^14 Hz. According to the Reference Table, an EM wave with that frequency would be visible light, specifically green light.
Question 71
Question 72
Since the jet had been travelling north and is decelerating, the direction of the acceleration is actually south. Since the magnitude of the acceleration is 2 m/s^2, the vector should be 4 cm long.
Question 73
Question 74
This is just one of the ways to solve this problem. In the official scoring key for this exam, the example answer uses F = ma instead of w = mg, but it’s essentially the same thing.
Question 75
Pay attention to the signs of the equation. Remember, when you subtract a negative, you actually add.
Question 76
For this question, all you have to do is convert your previous answer from e. V to J. Like with some of the earlier questions in this exam, if you get a wrong answer for the previous question, you can still get credit for this question as long as you do the conversion correctly.
