Answer & explanation
The official answer, with Fermi’s reasoning step by step.
Answer & explanation
Official answer
2,500
seconds
How to estimate it
Fermi’s official “Napkin math”
The Mariana Trench is about 11 kilometers deep, the lowest point in the ocean. How fast does a heavy iron ball sink? Maybe 4 or 5 meters a second.
- Trench depth
- 11,000 m
- Sink speed
- ~4.5 m/s
- 11,000 ÷ 4.5
- ≈ 2,500 sec
The Mariana Trench is about 7 miles deep, the lowest point in the ocean, which is around 36,000 feet. How fast does a heavy iron ball sink? Maybe 15 feet a second.
- Trench depth
- ~36,000 ft
- Sink speed
- ~15 ft/s
- 36,000 ÷ 15
- ≈ 2,400 sec
Rounded assumptions may give a slightly different estimate. The official answer above is the game’s reference value.
Source calculation & reference
- Trench depth
- ≈ 11,000 m
- Terminal velocity in water
- ÷ 4.4 m/s
- 11,000 ÷ 4.4
- ≈ 2,500 (~42 min)
Reference cited by Fermi: NOAA Challenger Deep depth · drag-equation estimate for a solid iron sphere
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