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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?

1 Answer

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by (51.5k points)
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Best answer

We have to first ind the retardation. 

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

as 

where: s = distance covered = 10 m 

v = final velocity = 0 m/s (brakes are applied so that buscomes to rest) 

u = initial velocity = 72 km/

h = 20 m/s 

a = acceleration = ? m/s2 

v2 – u2 = 2 

as 

0 – 202 = 2 × a × 10 

-400 = 20 × a 

\(\frac{400}{20}\)= 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 = 2 

as 

0 – 402 = 2 × -20 × s 

-1600 = -40 × s 

-\(\frac{1600}{-40}\)= s

s = 40 m

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