First, remember to multiply by 5 and divide by 18 to convert km/h to m/s. So, 72 km/h is exactly 20 m/s. For the bus problem, use this speed with the time given to find distance.
Just yesterday, my driving instructor was sternly pointing out my speed in km/h, but for the braking distance rule, he made me calculate it in metres per second—it makes the physics so much clearer for stopping in time on our crowded Bengaluru roads.
So, when you solve it, picture the actual bus and the metres it needs to stop safely, not just the number in the sum.
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