you get acceleration by differentiating v, if v is a function of t
a=dv/dt
if v is a function of x
a=dv/dx(1/2 v^2)
i hope i got the whole function thing right, because i always mix them up. when i say v is a function of x i mean v=2x+4 or whatever (just in case i didn't get the terminology right)
hope that helps but..