Question

Q. A bus is traveling at 72 km/hr. Brakes are applied and the bus comes to a stop after 10m. Find the retardation of the brakes.
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Answer 1

Answer:

As the bus comes to a stop later, its final velocity is 0 km/h or even can be written as 0 m/s.

retardation can also be written as acceleration.

a = ?

v = 0 km/h or 0 m/s

u = 72 km/h or 72*5/18

u= 4 *5 = 20 ( 72/18 = 4 )

u = 20 m/s

t = 10min ( 1min = 60 seconds

10min = 10*60 = 600 seconds)

t = 600s

a = v-u/t

a = 0-20/600

a = -20/600

a = -2/60

a = -1/30 m/s

or

_

a = 0.3 m/s

Answer 2

Answer:

The required retardation is 20 m/s².

Explanation:

Given :

A bus is traveling at 72 km/hr. Brakes are applied and the bus comes to a stop after 10 m.

To find :

the retardation of the brakes

Solution :

Initial velocity, u = 72 km/hr

u = 72 kmph

u = 72 × 5/18 m/s

u = 20 m/s

Final velocity, v = 0 m/s (rest)

Distance travelled, s = 10 m

Using v² – u² = 2as :

0² – 20² = 2(a)(10)

– 400 = 20a

a = –400/20

a = –20 m/s²

The acceleration is –20 m/s².

Retardation is the negative acceleration.

Therefore the retardation is 20 m/s².