Question

a bis travelling at 20m/sec is subjected to deaccelaration of 5m/sec how long it take to come at rest?

Answer 1

Use the equation v=u+at
Here
u=20 m/s
v=0 m/s (because the bus comes to rest)
a=(-5 m/s^{2}) (it's negative because it's in the direction opposite to the initial velocity u)

Using v=u+at,
         0=20+(-5)*t
         0=20-5t
        5t=20
          t= 4 seconds