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Unit 4 FRQ (Energy) Answers

4 min readβ€’november 29, 2021

AP Physics 1 🎑

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AP Physics 1 Free Response Question Answers for Energy

πŸ‘‹ Welcome to theΒ AP Physics Unit 4 FRQ (Energy) Answers.Β Have your responses handy as you go through the rubrics to see how you did!
⏱ Remember, the AP Physics 1 exam has 5 free-response questions, and you will be given 90 minutes to complete the FRQ section. (This means you should give yourself ~18 minutes to go through each practice FRQ.)


A projectile launcher consists of a spring with an attached plate, as shown in Figure 1. When the spring is compressed, the plate can be held in place by a pin at any of five positions A, B, C, D, or E.
For example, Figure 2 shows a ball placed against the plate, which is held in place by a pin at position A. The ball is launched upon release of the pin.
A student hypothesizes that the spring constant can be determined by launching the ball using different compression distances.

Questions with Answers & Rubric

Part A

(i) State a basic physics principle or law the student could use in designing an experiment to test the hypothesis. (1pt)

  • 1pt: Conservation of Energy

(ii) Using the principle or law stated in part (a) (i), determine (derive) an expression (physics equation) for the spring constant in terms of quantities that can be obtained from measurements made with equipment usually found in a school physics laboratory. (2pts)

πŸ“„ Additional Resources

Part B

Design an experimental procedure to test the hypothesis in which the student uses the launcher to launch the ball. Assume equipment usually found in a school physics laboratory is available.

(i) In the table below, list the quantities and associated symbols that would be measured in your experiment. Also, list the equipment that would be used to measure each quantity. (You do not need to fill in every row. If you need additional rows, you may add them to the space just below the table.) (3pts)

Quantity to be MeasuredSymbol for QuantityEquipment for Measurement

(ii) Describe the overall procedure to be used to test the hypothesis that the spring constant can be determined by launching the ball using different compression distances, referring to the table. Provide enough detail so that another student could replicate the experiment, including any steps necessary to reduce experimental uncertainty. As needed, use the symbols defined in the table and/or include a simple diagram of the setup. (5pts)

  • 1pt = Diagram
  • 1pt = SQuA (Measurement 1 & equipment)
  • 1pt = SQuA (Measurement 2 & equipment)
  • 1pt = Repeated Variable (Change the compression)
  • 1pt = Error Reduction (Do 3 trials for each pin, then average the compression values)

Part C

The student completes the experiment and obtains the data below. Using the data that most closely matches your experimental procedure, determine the spring constant for the spring.
Mass of Tennis Ball: 0.056 kg

(i) Using your expression in part (a) (ii), calculate the values that need to be plotted to find the spring constant for the spring and enter them into the data table above.

Pin LocationCompression (m)Maximum Height of Ball After Launch (m)Maximum Launch Speed of Ball Exiting Launcher (m/s)2mghmv^2x^2

(ii) Using the graph below, plot data from the data table that will allow the student to find the value for the spring constant.


(iii) Using your best-fit line, determine the spring constant for the spring in the space provided below.

πŸ“„ Additional Resources

Next Steps

  • 🧠 Want to continue reinforcing your knowledge of Unit 4? Check out Unit 4 Trivia, either as a document or as a game.
  • ⏭ Ready to move on to the next topic? Take a look at the collection of Unit 5 Resources.
  • πŸ“š Want to review multiple units? Check out all of the AP Physics 1 FRQs.
  • 🀝 Got more questions? Want to help others studying the same topic? Jump into a room in Hours!
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