A person starts to run at 12 m/s and then comes to a rest in 3s.
What is their velocity at 1 second

Velocity at 1 second = 8 m/s

Linear motion consists of 2: constant velocity motion with constant velocity and uniformly accelerated motion with constant acceleration  

• An equation of uniformly accelerated motion  

V = vo + at  

Vt² = vo² + 2a (x-xo)  

x = distance on t  

vo / vi = initial speed  

vt / vf = speed on t / final speed  

a = acceleration  

A person starts to run at 12 m/s and then comes to rest in  3s.

At rest vf=0

vi=12 m/s

t = 3 s