Question

and if a bus travel at 20 m per second is subjected to a declaration of 5 metre per second square how long will it take to come at rest

Answer 1

We know,equation of motion
V=u+at,
where,
v=final velocity
,u=initial velocity
,a=acceleration and
t=time elapsed
Here,bus will be finally coming to rest ,hence v=0
Initial velocity is given as u=20 and acceleration =a=-5(minus because retardation is there and velocity is decreasing)
We need to calculate t
V=u+at
0=20+(-5)t
0=20-5t
20=5t
T=4seconds