Given data

• Initial speed of bus: $72\ \text{km/h}$
• Final speed: $0$
• Time taken to stop: $4\ \text{s}$
• Retardation is uniform

Convert speed into SI unit $72\ \text{km/h} = 72 \times \frac{1000}{3600}\ \text{m/s} = 20\ \text{m/s}$

Use formula for distance under uniform acceleration/deceleration For uniform acceleration, distance is: $s = \frac{(u+v)}{2} \cdot t$ where

• $u = 20\ \text{m/s}$
• $v = 0\ \text{m/s}$
• $t = 4\ \text{s}$

Substitute values $s = \frac{20+0}{2} \times 4$ $s = 10 \times 4 = 40\ \text{m}$

Final answer The distance travelled by the bus is: $\boxed{40}$

Comparison with stored correct answer

• Derived answer: $40$
• Stored correct answer: $40$
• Both match.