Question

A bus moving with a speed 72km/h can be stopped by breaks after atleast 10 m. What will be the minimum stopping distance, if the same bus is moving at a speed of 144km/h?

Answer 1

Well, when we talk about breaking distance, we classify it into two types, the distance moved as the person thought about breaking and the distance it moved while breaking.
In order to solve the question, I will assume he acted immediately and therefore thinking distance is 0.
We have v^2=u^2+2as where,
v is final velocity which is when the vehicle has stopped hence v=0 m/s
u is initial velocity which is 72km/h or 20 m/s
s is 10m
Therefore the acceleration on the bus here is - 20 m/s which means it’s slowing down at that rate. If we assume that the breaking force is constant and the mass of the bus is unchanged, this is the maximum deceleration the bus can produce, regardless of speed.
We look back at the equation of motion again, v^2=u^2+2as where,
v= 0m/s
u=144km/h or 40m/s
a=-20m/s
Hence s which is the braking distance is 40 m.