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

We have to first find the retardation.
Using the third equation of motion: v2 – u2 = 2as
where: s = distance covered = 10 m
v = final velocity = 0 m/s (brakes are applied so that bus
comes to rest)
u = initial velocity = 72 km/h = 20 m/s
a = acceleration = ? m/s2
v2 – u2 = 2as

0 – 202 = 2 × a × 10

-400 = 20 × a

= a

a = -20 m/s2

Now, u = initial velocity = 144 km/h = 40 m/s
s = distance covered = ?? m
v = final velocity = 0 m/s ( brakes are applied so that bus comes to rest)
a = acceleration = -20 m/s2

Using the third equation of motion: v2 – u2 = 2as

0 – 402 = 2 × -20 × s

-1600 = -40 × s

= s

s = 40 m

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