(.140*25)+(75*0)= 3.5
3.5 = (.140 + 75)v
(3.5)/(.140 + 75) = v = .04657
which rounds up to .05 m/s
F=K*X,
F=M*a
M*a=K*X
2.5*9.81=K*0.0276
24.525=K*0.0276
24.525/0.0276=K
K= 888.6 N/m ---- force constant
assuming 2.5 refers to the new extension, just divide F/ 0.025
to get
981N/m
The minimum amount of force needed to move the ball is 15N