A motorist travelling at 72$kmh^{-1}$ had his eyes shut for 0.4s during a hard sneeze. Calculate the distance covered by him during this time interval.

Analyze the question: The motorist moves at a constant speed while his eyes are shut. We need the distance travelled in 0.4 s.

Concept: For constant speed, distance = speed × time. The units must match, so we convert km/h to m/s first.

Solution:

1. Convert the speed: 72 km/h = 72 × 1000 m / 3600 s = 20 m/s

(Shortcut: divide by 3.6, so 72 ÷ 3.6 = 20.)

2. Apply the formula: Distance = speed × time Distance = 20 m/s × 0.4 s = 8.0 m

Answer: The motorist covered 8.0 m, which is option D.

Tip: To convert km/h to m/s, divide by 3.6. To convert m/s to km/h, multiply by 3.6. Option B (28.8 m) is a trap: it comes from multiplying 72 × 0.4 without converting the units. Always check that your units match before calculating.