Velocity 等於0有加速度﹖

Any object (e.g. a car) that starts to move from rest would have a zero velocity and a non-zero acceleration.

Since acceleration a = (v-u)/t
where v and u are the final and initial velocities respetively, and t is the time interval.

When the object starts from rest, u =0 m/s
thus, a = v/t

hence, as long as v is not zero after time t (if v is zero, that means the object is at rest all the time), then a will have a certain value, i.e. non-zero acceleration.

velocity is the rate of change of displacement, i.e. the change of displacement per unit time. The instantaneous velocity is given by ds/dt - the first time-derivative of the displacement

In the s-t graph, the instantaneous velocity at time = t is actually given by the tangential slope at time =t.