Consider a particle of mass m that at time t=0 is at x=0 and traveling along the x-axis with a velocity v. It is described by a wave-packet of group velocity v and width w.
a) From the uncertainty principle, estimate the uncertainty in the velocity of the electron.
b) From the uncertainty in the velocity, estimate the
uncertainty in the position of electron, 
, as a
function of time t>0 as the wave-packet then begins to move.