Measuring Energy of Mass and Spring System

[sty2004]

Homework Statement

A mass m is connected to a spring of spring constant k. The equilibrium
position is x = 0 and the motion of the mass m is restricted by a stop such that
spring compression is not allowed, i.e., x < 0 is forbidden . The
system is in the ground state.
(a) The stop is suddenly removed and the energy is immediately measured.
What is the probability that the energy remains unchanged?
(b) If energy is measured after some delay from the instant the stop is
removed, will your answer be different?

Homework Equations

The Attempt at a Solution

 

[betel]

Nice question.
What are your ideas so far? Any relevant equations?
If you want us to help you, you have to give us a starting point where to help.

 

[jambaugh]

Your first step is to define the potential of the mass before and after the stop is removed.

Picture the SHO (simple harmonic oscillator) potential which is a parabolic well and then the "stop" cuts this parabolic well in half.

That's as much help as I can give without seeing any attempt or work.

 

[sty2004]

attempt:\Phi(x,0)=\sumc_n\phi_n
and c_n=<\phi|\Phi>
and then P=|c₁|²=|<\phi|\Phi(x,0)>|² ? what should be \phi ?