Question

A bus running at a speed of 18 kilometre per hour is stopped in 2.5 seconds by applying breaks calculate the retardation produced

Answer 1

Answer : retardation = 2 m/s

Explanation :
$v=u+at$
Here v = 0
         u = 18 km/h
            = 5 m/s
         t = 2.5 s
⇒ $a= \frac{v-u}{t}$
 a = (-5)/2.5
 a = -2 m/s
⇒ retardation = 2 m/s 

Answer 2

initial velocity, u = 18kmph = 5m/s { since all other values are given in MKS system this value should be converted}

the final velocity is zero ∴ v= 0
time = 2.5s
a=?
a= (v-u)/t
  = 0 -5/ 2.5
  -2m/s
here -ve sign implies it is retardation...

therefore the reatardation produced = 2m/s

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