Quite easy one again

let us take the frame of reference at the bottom of the jar

observe that at each moment more of the honey is moving upward( because the ball is going downwards)

so momentum of honey = mdx/dt m=mass of honey=volume*ρ

and x is the distance of com of honey from the bottom

let the distance of the steel ball be l from the bottom

then for finding the centre of mass of honey we can consider it as a negative mass in this case x=(m+M)(L/2)-M(l)/(m+M-M)

we know as it is moving with constant velocity
Mg=ρgV =>M=ρV

dx/dt=-M/(m)dl/dt but dl/dt=-v

mdx/dt=mMv/(m)

=Mv