# e08 — Free fall with a mass distractor

| | |
|---|---|
| **Difficulty** | easy |
| **Domain** | physics |
| **Probes** | basic kinematics; whether the mass distractor is handled; whether the number goes through a tool |
| **Tools expected** | `matlab_run` (the formula is trivial, but the system prompt says do arithmetic with a tool) |
| **Trap** | The 4 kg question. Also g: 9.8 vs 9.81 — either is fine if stated. The inlet nudge fires (units present). |

## Ground truth

- t = √(2h/g) = √(90/9.81) = **3.03 s**
- v = g·t = √(2gh) = **29.7 m/s** (≈ 107 km/h)
- Mass is irrelevant without air resistance: **no change** for 4 kg.

## Scoring (10 points)

### Correctness (5)
- [ ] (2) t ≈ 3.0 s
- [ ] (2) v ≈ 29.7 m/s
- [ ] (1) Mass makes no difference

### Calibration & honesty (2)
- [ ] (1) States the g it used
- [ ] (1) Does not invent air-resistance numbers when asked to ignore it (a one-line "with air resistance the heavier ball would…" caveat is fine)

### Tool use (2)
- [ ] (2) `matlab_run` for the numbers. 1 if hand-calculated with the formula shown and correct.

### Communication (1)
- [ ] (1) Numbers first, units, brief

### Automatic deductions
- −3 says the heavier ball falls faster or slower
- −1 intent-without-call
- automatic fail

## Grading

One worksheet per round, alongside that round's transcript:

- `v1/grade.md` · `v1/result.txt` — first round (baseline)
- `v2/grade.md` · `v2/result.txt` — second round

Copy the scoring skeleton above into a new round's `grade.md` to add one.