Question

When brakes are applied to a bus the retardation produced is 25cm/s*s and the bus takes 20 a to stop. Calculate :1)initial velocity 2)acceleration of car

Answer 1

Retardation (-a) = - 25 cm/s2 
Time taken to get stopped (tav)=20 second
As the bus starts from rest, 
∴ final velocity (v)= 0
Initial velocity (u)= ?
Distance(s) = ? 
First we will calculate initial velocity of the bus.
We know 
a = (v - u ) / t
Or - 25 = (0 - u )/ 20 
Or -25 = - u /20
Or u = 25x 20 
∴ u = 500 cm/s
Or u = (500/100) m/ s
Or u= 5 m/s 

Again We know that:
s = ut + 1/2 a. t2 
or S = 10000 - 1/2 .25. 400
or S = 10000 - 5000
or S = 5000 cm
or S = 50 m
∴ Initial velocity (u) = 5m/s and
Distance (s)=50m Answer