Physics · Unit 1: Kinematics ·  Activity 1-2-2

Equation Detective

🧩 Activity
2 class days  ·  Work in pairs
Activity 1-2-2: The Kinematic Equations

Four equations, five variables, zero guessing. Today's job is to get fast and reliable at spotting which variable a problem leaves out — because that's the entire trick to picking the right equation, every time, without memorizing "types" of problems.

🎯 Goals

🧰 Materials

🃏Scenario cards (Day 1 card sort)
📄Multi-step relay handout (Day 2)
🧮Calculator
📓Physics notebook
DAY 1
The Card Sort
Section 1 of 4

Sort the Scenario Cards

1
Read each scenario card and list the variables it gives you.
Write down exactly what's stated — a value, a unit, and which of the five variables it represents.
2
Identify what the card is asking you to find, and which variable never appears at all.
Three variables given, one variable wanted, and one variable completely absent from the card — that absent one is your signal.
⚠️ Watch for variables in disguise — 'starts from rest' means v₀ = 0, and 'comes to a stop' means the final v = 0. Both are still given information, just worded differently.
3
Sort each card to the equation that matches its missing variable.
Use the missing-variable table from the Deep Dive if you need it.
Card 1. A skater speeds up from 3 m/s to 9 m/s over 4 s. How far did she travel?
given
missing
equation
answer
Card 2. A ball is dropped and falls for 2 s with a = 9.8 m/s². What's its final velocity?
given
missing
equation
answer
Card 3. A car goes from 0 to 20 m/s over a distance of 50 m. What was its acceleration?
given
missing
equation
answer
Card 4. A cyclist travels 40 m while decelerating from 8 m/s to 2 m/s. How long did it take?
given
missing
equation
answer

In-class scratch space — copy your final sort and answers onto your handout to turn in.

📓 Physics Notebook
Pick one card where the missing variable surprised you at first. What made it tricky to spot, and what will you look for next time to catch it faster?
DAY 2
The Multi-Step Relay
Section 2 of 4

Set Up the Relay

4
Read your team's multi-step scenario all the way through before writing anything.
These describe motion happening in two or three distinct stages — notice where one stage ends and the next begins.
5
Solve Stage 1 completely before touching Stage 2.
Identify the missing variable for Stage 1 only, solve for whatever it asks, and hold onto that answer.
Section 3 of 4

Carry the Answer Forward

6
Use Stage 1's result as a known value in Stage 2.
This is the whole point of a multi-step problem — the quantity you just solved for becomes one of the three knowns for the next stage's equation.
7
Repeat for every remaining stage, then combine results if the final question asks for a total.
Some relay questions want a single stage's answer; others want something combined across all stages, like total displacement.
StageGiven (incl. carried-over)FindEquation usedResult
Stage 1
Stage 2
Stage 3 (final answer)

Each stage's Result should feed into the next stage's Given — that's the whole point of the relay.

📓 Physics Notebook
At which stage transition did you almost use the wrong equation, and what tipped you off that something was wrong before you finished the calculation?
Section 4 of 4

Conclusion

Question 1
Explain the missing-variable strategy in your own words — how do you decide which of the four equations to use without memorizing 'types' of problems?
Question 2
One of the four equations doesn't require time at all. Describe a real situation where you'd be given distance and both velocities but never told how long the motion took, and explain why that equation is exactly what you'd need.
Question 3
Why do all four equations assume constant acceleration, and what would go wrong if you used them for a motion where the acceleration was actually changing?
📤 Turn In
← Back to Activity 1-2-2 OverviewReview the Deep Dive →Next up: Project 1-2-3, Reconstruct the Ride.