Is Velocity Equal to a*t in an Acceleration vs Time Graph?

[ahmed emad]

is the velocity at t=0 in acceleration vs time graph must be 0 .please answer my question

 

[Chestermiller]

Not necessarily.

 

[ahmed emad]

Not necessarily.

but why the velocity = a*t so v=4*0=o m/s

 

[Chestermiller]

but why the velocity = a*t so v=4*0=o m/s

$$v=v_0+at$$