Spring Acceleration: Does Velocity = 0 Mean a = 0?

[IKonquer]

Lets say you attach a weight to a spring and release it from rest. When the spring reaches its lowest point, its velocity is zero. What I am confused about is the acceleration of the spring at the bottom. My professor said that the acceleration of the weight at the bottom is g upwards. Intuitively that makes sense to me but not mathematically. dv/dt = a. And if the velocity is 0 at that instant, shouldn't the acceleration also be zero?

Thanks in advance.

 

[zorro]

a=dv/dt is right. But since the mass executes S.H.M, a=-ω²x.
When the mass reaches its lowest point, x is not 0. Infact, x is max and hence a is max.
Acceleration is instantaneosly 0 only when it crosses its mean position.