Physics 1 FRQ Walkthrough: Describe, Explain, Justify — A Student’s Guide to Top-Scoring Responses

Why FRQs Matter — and Why Language Is Everything

If you’re preparing for AP Physics 1, you already know the multiple-choice questions test your recall and quick problem solving. But the free-response questions (FRQs) are where you show depth: your reasoning, your ability to translate physics concepts into words, diagrams, and math. College Board doesn’t just want a number — it wants a clear chain of reasoning. That’s why verbs like “describe,” “explain,” and “justify” are clues about what the graders expect.

Understanding the Command Words: Describe, Explain, Justify

Before diving into tactics and examples, let’s translate those command words from exam-speak into student-friendly tasks.

Describe

When the prompt asks you to describe, the grader wants observable or definable features. Think: what happens, what you see, or which variables change. Descriptions are concrete and often qualitative. Keep them precise and tied to the system in the question.

Explain

Explain asks you to link cause and effect. This is where you connect physical laws, principles, or equations to the situation. Explanations are logical narratives: lead the reader from assumptions to conclusion using physics concepts (Newton’s laws, conservation laws, kinematics, etc.).

Justify

Justify is the strongest ask: you must present evidence, reasoning, or calculations that back up your claim. Justification often merges a concise explanation with supporting math, units, or a reference to data in the problem.

Three Core Principles for All FRQ Responses

No matter the question type, strong FRQ answers follow three consistent habits:

• Structure your response. Use short labeled steps (e.g., Step 1: Identify knowns) so graders can follow your logic.
• Be explicit with assumptions. If you assume frictionless motion or negligible air resistance, say so.
• Include units, vector directions, and significant relationships. Units are not optional; direction matters in vector problems.

A Walkthrough: Typical FRQ Types and How to Answer Them

The AP Physics 1 FRQs often test a handful of question archetypes. Below, we’ll walk through each archetype with a mini-strategy and an example of what graders want.

1) Kinematics and Dynamics — Describe Motion, Explain Forces

Task: Link motion graphs, acceleration, and net force. Graders want clear statements about direction and cause.

Strategy:

• Start by defining a coordinate system (positive direction) and listing known values.
• Describe the motion qualitatively (increasing speed, constant velocity, changing direction).
• Explain with Newton’s laws: identify forces, write ΣF = ma, and indicate direction explicitly.
• If asked to justify, show the algebraic step that connects forces to acceleration and match signs/directions.

Example phrasing that earns points:

• “Using rightwards as positive, the velocity increases in the rightwards direction, so acceleration is rightwards and positive.”
• “The net force is to the right because the applied force (Fapplied) exceeds friction (f), so ΣF = Fapplied − f = ma, giving a = (Fapplied − f)/m.”

2) Energy and Work — Describe Energy Changes, Justify Conservation

Task: Link work done, potential and kinetic energy changes, and conservation statements.

Strategy:

• Identify system boundaries and state whether non-conservative forces (like friction) do work.
• Write energy relationships: ΔKE = Wnet or KEi + PEi + Wnonconservative = KEf + PEf.
• If asked to explain, show algebra connecting heights, speeds, and work.

Example phrasing:

• “Because no non-conservative work is performed, mechanical energy is conserved: ½mv_i^2 + mgh_i = ½mv_f^2 + mgh_f. Solving yields v_f = sqrt(v_i^2 + 2g(h_i − h_f)).”

3) Conservation Laws and Collisions — Explain and Justify Using Equations

Task: Use conservation of momentum and possibly kinetic energy. Highlight inelastic vs. elastic outcomes.

Strategy:

• State which quantities are conserved (momentum always in isolated system; kinetic energy only if elastic).
• Set up the relevant equations: Σp_initial = Σp_final and, if elastic, ½m1v1^2 + ½m2v2^2 conserved.
• Justify each algebraic manipulation and check units for velocity or momentum.

4) Experimental Design and Analysis — Describe Procedure, Justify Controls

Task: Propose or critique an experiment, identify variables, and justify controls and uncertainty analysis.

Strategy:

• Clearly state the measurable independent and dependent variables and at least one controlled variable.
• Describe the data collection method and explain how it isolates the effect under study.
• Include a brief uncertainty analysis or how to reduce systematic and random errors.

Example phrasing:

• “Independent variable: angle θ. Dependent variable: range R. Control: initial speed and launch height held constant by using the same launcher setting and fixed platform height.”
• “To reduce random error, repeat each trial three times and use the mean; to reduce systematic error, calibrate the launcher velocity using a photogate.”

How to Write Answers That Earn Full Points

Let’s turn strategy into an actionable checklist you can apply on test day.

• Label each part of your answer (a), (b), etc. Graders are human and will thank you for clarity.
• Start with a one-sentence conclusion when asked to describe or explain. Then show the reasoning. Example: “Conclusion: The block accelerates to the right at 1.5 m/s².”
• When you use an equation, briefly state why it applies (e.g., “use conservation of momentum because external horizontal forces are negligible”).
• Write units every time you provide a numeric value.
• Make quick diagrams if helpful — label forces, velocities, and positive directions. A tidy diagram can earn a point even if algebra is imperfect.

Sample FRQ Walkthrough — Putting It All Together

Below is a compact, genuine-style example and a model student response that demonstrates Describe / Explain / Justify steps.

Sample Prompt (paraphrased)

A block of mass m is attached to a spring (spring constant k) on a frictionless horizontal surface. The block is pulled to the right and released from rest at displacement x0. (a) Describe the motion of the block. (b) Explain how the energy changes as the block moves from x0 to equilibrium. (c) Justify that the maximum speed occurs at the equilibrium position and calculate that speed.

Model Answer — Step by Step

(a) Describe the motion. Using rightwards as positive, the block oscillates about the equilibrium position with simple harmonic motion (SHM). The displacement varies sinusoidally between +x0 and −x0, and the speed is maximal at equilibrium and zero at the turning points.

(b) Explain energy changes. Initially at x0 the block has maximum spring potential energy (½kx0²) and zero kinetic energy. As the block moves toward equilibrium, spring potential energy decreases while kinetic energy increases. At equilibrium, spring potential energy is minimal (zero) and kinetic energy is maximal, with mechanical energy conserved throughout because the surface is frictionless.

(c) Justify maximum speed at equilibrium and calculate it. Conservation of mechanical energy applies: ½k x0² = ½m v_max². Solving for v_max gives v_max = x0 sqrt(k/m). Units check: sqrt(N/m ÷ kg) × m = m/s, which is consistent. The conclusion follows because all potential energy at the turning point converts to kinetic energy at equilibrium, justifying why speed peaks there.

Common Mistakes and How to Avoid Them

These errors are frequent — and avoidable.

• Missing units on numerical answers. A number without units often loses a point.
• Sign confusion in vector problems. Always declare your positive direction and stick to it.
• Using an equation without justifying its applicability (e.g., applying energy conservation without addressing non-conservative forces).
• Forgetting to state controlled variables in experimental design prompts.
• Messy diagrams. If you draw it, label it clearly — force vectors, axes, and typical values help.

Quick-Tips Table — At-A-Glance Reference

How to Practice Efficiently — Realistic Drills

You don’t need to solve every past FRQ. Instead, use targeted practice with the following routine:

• Pick one FRQ archetype per study session. Time yourself (about 15–25 minutes for most parts) and simulate exam conditions.
• Write out concise answers using the structure: Statement, Reasoning, Calculation, Units. Keep handwriting legible.
• After finishing, compare your logic to scoring guidelines if available. If a rubric isn’t accessible, check your work against the core physics principles and unit consistency.
• One week before the exam, do full timed practice (100 minutes for 4 FRQs) to build stamina and pacing.

Using Feedback to Improve Faster

Practice matters most when paired with targeted feedback. A tutor or teacher can highlight recurring issues: weak justifications, algebraic missteps, or unclear English. Even a single session focusing on FRQ structure can yield dramatic improvements.

If you want structured 1-on-1 guidance, Sparkl’s personalized tutoring offers tailored study plans, expert tutors who can walk through your FRQs line by line, and AI-driven insights that point out recurring weak spots so you don’t repeat old mistakes. A couple of tutoring sessions focused on FRQ writing style and justification can make your responses cleaner and more persuasive.

Exam-Day Strategy: From Arrival to Submission

On test day, your calm is as important as your physics knowledge. Here’s a stepwise plan to maximize your score:

• Read all FRQs quickly (5–7 minutes) and mark the ones you find straightforward vs. those that will need more setup.
• Tackle one you know well first to lock in points and build confidence.
• For each part, write a one-line conclusion before calculation. That helps graders see your main claim even if algebra slips.
• If stuck, move on and return — graders can’t penalize you for incomplete work if the parts you did are clear and correct.
• Leave 5–10 minutes to check units, signs, and clarity of explanations.

Final Thoughts — Your Voice in Physics

AP Physics 1 FRQs test more than formulas. They test your ability to communicate physics: to describe phenomena clearly, to explain using cause-and-effect anchored in laws, and to justify claims with equations or evidence. Think of every FRQ as a mini scientific argument. State your claim, back it with reasoning, and seal it with math or measurement.

The good news? These are skills you can build. Start by following the structure: Declare, Support, Calculate, Check. Draw neat diagrams. Practice under timed conditions. And if you want extra concentrated help, consider targeted sessions with a tutor — for example, Sparkl’s 1-on-1 coaching can help you refine phrasing, tighten justifications, and develop a personalized study plan so your practice time gives you the highest return.

Approach the exam the way a scientist writes: clearly, honestly, and with the confidence that comes from preparation. You don’t need to sound fancy — you need to be precise. When your writing mirrors your understanding, the points follow.

Takeaway Checklist

• Always label axes and directions.
• Begin answers with a one-sentence conclusion.
• State applicable physics principles and justify why they apply.
• Include units and perform a quick units check.
• Use diagrams where helpful and keep them labeled.
• Practice with feedback; consider a few 1-on-1 sessions for rapid improvement.

You’re Ready — Now Go Write Great Answers

FRQs reward clarity. Show your reasoning like a story with clear steps, and you’ll make life easy for the grader — and yourself. Good luck on exam day, and remember: with steady practice and crisp explanations, you can turn tricky prompts into points. If you’d like, I can create a personalized 4-week FRQ practice plan tailored to your strengths and weaknesses.