AP Physics 1 2015 Free Response Solutions
TLDRIn this video, Dan Fullerton tackles the 2015 AP Physics 1 free response questions, offering insights into problem-solving strategies and the thought process behind deriving solutions. He covers a range of topics, from freebody diagrams and Newton's laws to wave velocities and energy transformations in circuits. Fullerton emphasizes the importance of understanding fundamental physics concepts and applying them to real-world scenarios, all while providing a clear and coherent explanation of complex topics.
Takeaways
- π The video discusses solving 2015 AP Physics 1 free response questions without official solutions for reference.
- π For question 1, Freebody diagrams are drawn for blocks hanging from a table with massless pulleys, and the acceleration of block 2 is derived using Newton's second law.
- π In part B, the addition of a third block in the middle results in a smaller acceleration for block 2 due to the increased mass of the system.
- π‘ Question 2 explores energy consumption in an incandescent light bulb and the experimental procedure to determine electron behavior and electric potential energy changes.
- π§ The setup for question 2 involves a series circuit with an ammeter and voltmeter to measure current and voltage across the light bulb.
- π Data analysis for question 2 includes plotting voltage across the bulb versus current to determine if the light bulb follows Ohm's law.
- π’ For question 3, graphs of potential energy for a block-spring system are sketched, illustrating the transformation of potential to kinetic energy.
- π€ The student's reasoning in part 3b is partially correct; the block will slide further with more energy from the compressed spring, but it will stop at x=12D, not x=6D, due to the quadrupling of elastic potential energy.
- π In question 4, two spheres are released from the same height with one dropped vertically and the other projected horizontally; they reach the ground simultaneously due to identical vertical motion.
- π The horizontal component of velocity for the spheres in question 4 remains constant for the horizontally projected sphere and is zero for the dropped sphere.
- πΌ Question 5 examines strings of different fundamental frequencies, with the key difference being the linear mass density (mass per unit length) of the strings.
- π The graph of frequency versus the inverse of linear mass density for the strings in question 5 is expected to be linear because frequency is proportional to the square root of the tension force divided by the linear mass density.
Q & A
What is the main goal of the video?
-The main goal of the video is to analyze the 2015 AP Physics 1 free response questions and provide a first pass at solutions, offering insights into what the exam is looking for and how to approach answering such questions.
How does the speaker plan to handle the writing of answers in the video?
-The speaker plans to highlight key points that would be expected in an answer rather than writing out full answers to all the questions, especially for questions that require a paragraph response.
What is the first scenario described in the video?
-The first scenario described is a system with multiple blocks hanging from a table with massless pulleys connected by a string, and the task is to draw Freebody diagrams for each block and derive the magnitude of the acceleration of block 2.
How does the speaker approach the Freebody diagrams for the blocks in the first question?
-The speaker starts by looking at the forces acting on each block, considering the tension in the string and the weight of the blocks, and expects the tension to be slightly larger than the weight for the first block and significantly larger for the second block.
What is the derived acceleration of block 2 in the first question?
-The derived acceleration of block 2 is (m2 - m1) / (m1 + m2) times the acceleration due to gravity (g), based on the analysis of the forces acting on the two blocks and the application of Newton's second law.
How does the speaker describe the experimental setup for question 2?
-The speaker describes a series circuit with an ammeter to measure the current and a voltmeter to measure the electric potential difference across the light bulb, to investigate what gets used up in an incandescent light bulb and whether the electric potential energy of electrons changes inside the bulb.
What is the main focus of question 3?
-The main focus of question 3 is to analyze the motion of a block with a spring on a frictionless surface, initially compressed, and then released, sketching graphs of the block's potential energy and the block-spring system's potential energy as a function of position.
What is the student's reasoning in question 3b, and what is incorrect about it?
-The student's reasoning is that doubling the spring's compression would mean the block has more energy when released, so it will slide farther along the track. The incorrect aspect is stating that the block will stop at x = 6D; instead, it should stop at x = 12D, as doubling the compression quadruples the stored elastic potential energy.
How does the speaker address the projectile motion in question 4?
-The speaker addresses the projectile motion by sketching Freebody diagrams for two spheres released from the same height, one dropped vertically and the other projected horizontally, and explaining why they reach the ground at the same time despite traveling different distances, focusing on the independence of horizontal and vertical motion and the same acceleration due to gravity.
What is the key difference in the strings' properties in question 5 that leads to different fundamental frequencies?
-The key difference is the mass per unit length (linear mass density) of the strings, which must be different for each string to result in different fundamental frequencies, given that the length and mass of the blocks are the same.
How does the speaker describe the relationship between frequency and linear mass density in question 5?
-The speaker describes the relationship as a linear graph of the square of frequency (f^2) versus the inverse of linear mass density (1/M over L), based on the derived equation from the wave speed formula and the relationship between frequency, wave speed, and wavelength.
Outlines
π Physics Problem Solving Strategy
The speaker, Dan Fullerton, introduces his approach to solving the 2015 AP Physics One free response questions. He acknowledges that he hasn't seen the official solutions, so there might be minor errors in his explanations. His strategy involves going through the problems, identifying key points, and providing a first pass at potential solutions. He also discusses how to approach answering questions that require writing paragraphs by highlighting the essential points expected in an answer.
π Analyzing a Circuit with a Light Bulb
In this section, the speaker addresses a question about an incandescent light bulb in a circuit with a resistor. The focus is on understanding what gets used up in the light bulb and whether the electric potential energy of electrons changes inside the bulb. The speaker proposes an experimental setup involving ammeters and voltmeters to measure current and voltage. He explains how to use the equipment and interpret the data to answer the questions about electron behavior and electric potential energy changes within the light bulb.
π Interpreting Graphs of Potential Energy
The speaker tackles a problem involving a block with a spring on a frictionless surface. He explains how to sketch and label graphs of the potential energy of the block and the block-spring system as a function of position. The speaker provides a detailed analysis of how the potential energy changes as the block moves from a compressed to an expanded position. He also addresses a student's reasoning about the final position of the block when the spring is compressed twice as much and corrects the student's misconceptions with quantitative reasoning.
π Projectile Motion of Identical Spheres
This paragraph discusses a projectile motion problem involving two identical spheres released from the same height. One sphere is dropped vertically, while the other is projected horizontally. The speaker explains how to draw Freebody diagrams for each sphere and how to sketch a graph of the horizontal component of velocity as a function of time. He then provides a clear, coherent explanation of why both spheres reach the ground at the same time, despite traveling different distances, emphasizing the independence of horizontal and vertical motion and the same acceleration due to gravity.
π΅ Harmonic Oscillation and Wave Properties
The speaker explores a problem related to harmonic oscillation and wave properties on a string with a mass attached to one end. He discusses how different fundamental frequencies can be achieved by altering the linear mass density of the string. The speaker also explains how to graph frequency versus the inverse of linear mass density and predicts a linear relationship due to the square of frequency being proportional to the tension divided by the square of wavelength times the inverse of linear mass density. Lastly, he describes how to identify points on the string with the greatest average vertical speed when the string vibrates in its second harmonic.
Mindmap
Keywords
π‘Freebody diagrams
π‘Newton's second law
π‘Acceleration
π‘Incandescent light bulb
π‘Electric potential energy
π‘Ohm's law
π‘Spring potential energy
π‘Projectile motion
π‘Wave velocity
π‘Standing wave
π‘Linear mass density
Highlights
The video discusses solving 2015 AP Physics 1 free response questions.
The presenter, Dan Fullerton, has not seen the official solutions or scoring guide, so there might be minor errors in the solutions.
For question 1, the task is to draw Freebody diagrams for blocks hanging from a table with massless pulleys and strings.
In part B of question 1, the derivation of the acceleration of block 2 is based on Newton's second law and the forces acting on the blocks.
The acceleration of block 2 is smaller when a third block is added due to the increased mass of the system.
Question 2 involves a circuit question about an incandescent light bulb in series with a resistor.
The experimental procedure to answer what gets used up in an incandescent light bulb involves using ammeters and voltmeters.
The data from the experiment can be used to determine if the electric potential energy of electrons changes inside the light bulb.
The question on whether the light bulb is ohmic or non-ohmic is addressed by analyzing the plot of voltage across the bulb versus current.
In question 3, a block with a spring on a table is released and experiences friction, with the graphs of potential energy and kinetic energy being key.
The student's reasoning about the block's final position when the spring is compressed twice as much is partially correct, and the quantitative reasoning is provided to correct it.
The mathematical relationships in part C of question 3 correct the student's incorrect reasoning by showing that the new distance is twelve times D.
In question 4, two spheres are released from the same height, one dropped and one projected horizontally, and their Freebody diagrams are discussed.
The spheres reach the ground at the same time due to the independence of horizontal and vertical motion, which is explained in a paragraph length response.
Question 5 involves a string attached to an oscillator and a block, with different fundamental frequencies for each string.
The difference in the fundamental frequency of the strings is due to the different mass per unit length, as explained in part A of question 5.
The graph of frequency versus the inverse of linear mass density is expected to be linear, based on the wave speed equation.
When the string vibrates in its second harmonic, the points on the string with the greatest average vertical speed are labeled as antinodes.
The video concludes by summarizing the solutions to the AP Physics 1 free response questions.
Transcripts
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