A LiDAR takes 400 ns from emitting a laser pulse until the reflected light returns from an object. Approximately how far away is the object? (speed of light 3×10⁸ m/s)

Answer: B. 60 m

Light travels to the object and back, so distance is speed of light × time ÷ 2. 3×10⁸ m/s × 400×10⁻⁹ s = 120 m is the round-trip distance, so the one-way distance is 60 m. 120 m is the value obtained by forgetting to divide by 2. Measuring distance from the round-trip time of light in this way is called ToF (Time of Flight). LiDAR can measure 3D shapes with high resolution, but its performance tends to degrade in dense fog or heavy rain as light scatters, and cost is also a challenge.