{
  "correct_letter": "B",
  "correct_formula": "v = v_0 + g·t",
  "annotation": "Environment: g=9.81, F_drag=!=0\nGround: e=0.5\nTennisBall: d = 0.07, e = 0.75, h = 1.68, v_0 = 3.92",
  "choices": [
    "I = (1/10)·m·d²",
    "v = v_0 + g·t",
    "T = 2π·√(m/k)",
    "y(t) = h·(1 - e^(-g·t²/2))"
  ],
  "correct_index": 1,
  "physics_type": "FreeFall",
  "seed": "FreeFall|Gravity/Freefall/21",
  "is_realworld": true,
  "dropped_wrong_formulas": [
    "P + (1/2)·ρ·v² + ρ·g·h = constant"
  ]
}