Learn Extracted exam questions AP Physics 2 2019 Free Response
2019 Free Response
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The figure above shows a particle with positive charge $+Q$ traveling with a constant speed $v_0$ to the right and in the plane of the page. The particle is approaching a region, shown by the dashed box, that contains a constant uniform field. The effects of gravity are negligible.
[Figure: A diagram labeled "Region of Field" shows a dashed square box on the right. To the left, a dot labeled "Particle" with "$+Q$" beneath it has an arrow labeled $v_0$ pointing right toward the box.]
On the figure below, draw a possible path of the particle in the region if the region contains only an electric field directed toward the bottom of the page.
[Figure labeled "Electric Field": a dashed square box on the right; to the left, a dot with an arrow pointing right toward the box.]
On the figure below, draw a possible path of the particle in the region if the region contains only a magnetic field directed out of the page.
[Figure labeled "Magnetic Field": a dashed square box on the right; to the left, a dot with an arrow pointing right toward the box.]
For which of the previous situations is the motion more similar to that of a projectile in only a gravitational field near Earth's surface, and why?
Another region of space contains an electric field directed toward the top of the page and a magnetic field directed out of the page. Both fields are constant and uniform. A horizontal beam of protons with a variety of speeds enters the region, as shown above. Protons exit the region at a variety of locations, including points 1 and 2 shown on the figure. In a coherent, paragraph-length response, explain why some protons exit the region at point 1 and others exit at point 2. Use physics principles to explain your reasoning.
[Figure: "Proton Beam" with an arrow entering a dashed square box from the left. Inside the box, rows of dots (field out of page) with two upward arrows in the middle (electric field direction inside region); the right edge of the box has two exit points marked "1" (upper) and "2" (lower). To the right of the box, a legend shows a dot labeled "Magnetic Field Out of Page" and an upward arrow labeled "Electric Field Toward Top of Page".]
[Figure: Two circuit diagrams side by side. "Circuit 1": An ideal variable power supply $V_{PS}$ (circle with battery symbol) connects in a loop to an ammeter A (circle) in series with the top branch, a resistor $R$ in series with a voltmeter $V_R$ on the right branch, all in parallel with $V_{PS}$. "Circuit 2": Same layout as Circuit 1, except the ammeter A is drawn inside a dashed box together with a zigzag resistor symbol labeled (representing internal resistance), indicating the ammeter has significant internal resistance.]
The two circuits shown above contain an ideal variable power supply, an ohmic resistor of resistance $R$, an ammeter A, and two voltmeters $V_{PS}$ and $V_R$. In circuit 1 the ammeter has negligible resistance, and in circuit 2 the ammeter has significant internal ohmic resistance $r$. The potential difference of the power supply is varied, and measurements of current and potential difference are recorded.
The axes below can be used to graph the current measured by the ammeter as a function of the potential difference measured across the power supply. On the axes, do the following.
- Sketch a possible graph for circuit 1 and label it 1.
- Sketch a possible graph for circuit 2 and label it 2.
[Graph: y-axis labeled "Current", x-axis labeled "Power Supply Potential Difference", origin labeled $O$; blank axes with no data plotted, to be filled in by the student.]
Let $\Delta V_{PS}$ be the potential difference measured by voltmeter $V_{PS}$ across the power supply, and let $I$ be the current measured by the ammeter A. For each circuit, write an equation that satisfies conservation of energy, in terms of $\Delta V_{PS}$, $I$, $R$, and $r$, as appropriate.
Circuit 1: _______________________
Circuit 2: _______________________
Explain how your equations in part (b) account for any differences between graphs 1 and 2 in part (a).
In circuit 2, $R = 40\ \Omega$. When voltmeter $V_{PS}$ reads 3.0 V, voltmeter $V_R$ reads 2.5 V. Calculate the internal resistance $r$ of the ammeter.
Voltmeter $V_R$ in circuit 2 is replaced by a resistor with resistance $120\ \Omega$ to create circuit 3 shown below. Voltmeter $V_{PS}$ still reads 3.0 V.
[Figure "Circuit 3": A power supply $V_{PS}$ (circle with battery symbol) in a loop with an ammeter A in a dashed box together with a zigzag resistor labeled $r$ in the top branch, in parallel with a $40\ \Omega$ resistor and a $120\ \Omega$ resistor, both shown as parallel branches on the right.]
Calculate the equivalent resistance $R_{eq}$ of the circuit.
Calculate the current in each of the resistors that are in parallel.
[Figure: A diagram of an apparatus. From top to bottom: a block labeled "Ice" sits on top of a layer labeled "Slab of Plastic"; below that is a dark rectangle labeled "Hot Plate" on the left with "Container of Boiling Water" labeled to its left; a small container to the right labeled "Water Collected" catches a drip from the slab, shown with a shaded region at the bottom of that container.]
A group of students use the apparatus shown above to determine the thermal conductivity of a certain type of plastic. A hot plate is used to keep water in a container boiling at a temperature of $100^\circ\text{C}$. They place a slab of the plastic with area $0.025\ \text{m}^2$ and thickness $0.010\ \text{m}$ above the container so that the bottom surface of the slab is at a temperature of $100^\circ\text{C}$. They put a large block of ice with temperature $0^\circ\text{C}$ on top of the plastic slab. Some of the ice melts, and the students measure the amount of water collected during a time $\Delta t$. The students correctly calculate the amount of energy $Q$ delivered to the ice and thus determine $Q/\Delta t$. They repeat this experiment several times, each time adding an identical slab to increase the total thickness $L$ of plastic. Their results are shown in the table below.
| Energy flow rate $Q/\Delta t$ (J/s) | 97 | 53 | 31 | 27 | 18 |
|---|---|---|---|---|---|
| Total thickness of plastic $L$ (m) | 0.010 | 0.020 | 0.030 | 0.040 | 0.050 |
The students want to create a graph to yield a straight line whose slope could be used to calculate the thermal conductivity of the plastic.
Label the axes below to indicate a pair of quantities that could be graphed to yield a straight line. Include units for the quantities.
[Figure: A blank grid with axes to be labeled by the student, gridlines shown but no data plotted, no axis labels or scale provided.]
On the grid on the previous page, create a linear graph using the values for the quantities indicated in part (a)(i). Be sure to do the following.
- Add to the data table the values of any quantities to be plotted that are not already given.
- Scale the axes.
- Plot the data from the table.
- Draw a line that best represents the data.
Use the graph to calculate the thermal conductivity of the plastic.
Indicate one potential problem with the setup that could lead to an experimental value for the thermal conductivity that is different from the actual value. Use physics principles to explain the effect this problem could have on the experimental value.
The rectangle below represents a side view of the plastic slab. Draw a single arrow on the diagram representing the direction of the net flow of energy through the plastic.
[Figure: A blank rectangle labeled "Plastic Slab" at the bottom right, representing a side view of the slab, with no arrow drawn.]
Describe what occurs in the plastic at the microscopic level that explains the energy flow you indicated in part (c).
An extra plastic slab sits on a wood surface, with both the plastic slab and the wood surface at room temperature. A student touches each and finds that the plastic slab feels cooler than the wood surface. Explain what causes this observation.
A student notices many air bubbles rising through the water in a large fish tank at an aquarium.
In the figure below, the circle represents one such air bubble, and two incoming rays of light, A and B, are shown. Ray B points toward the center of the circle. On the diagram, draw the paths of rays A and B as they go through the bubble and back into the water. Your diagram should clearly show what happens to the rays at each interface.
[Figure: A large circle labeled "Air" on the right side, with "Water" labeled to its left outside the circle. Two horizontal rays labeled A (upper) and B (lower) enter from the left and strike the circle's boundary; ray B is aimed at the center of the circle. Arrowheads show the rays traveling rightward toward the circle.]
The bubble has a volume $V_1$, the air inside it has density $\rho_A$, and the water around it has density $\rho_W$. The bubble starts at rest and has a speed $v_f$ when it has risen a height $h$. Assume that the change in the bubble's volume is negligible. Derive an expression for the mechanical energy dissipated by drag forces as the bubble rises this distance. Express your answer in terms of the given quantities and fundamental constants, as appropriate.
At a particular instant, one bubble is 4.5 m below the water's surface. The surface of the water is at sea level, and the density of the water is $1000\ \text{kg/m}^3$.
Determine the absolute pressure in the bubble at this location.
The bubble has a volume $V_1$ when it is 4.5 m below the water's surface. Assume that the temperature of the air in the bubble remains constant as it rises. In terms of $V_1$, calculate the volume of the bubble when it is just below the surface of the water.
If the air in the bubble cooled as it rose, the volume of the bubble would be less than the value calculated in part (c)(ii). Use physics principles to briefly explain why.