Finding Force and Distance in Simple Harmonic Motion Problem

[Kefurinu]

Homework Statement

A box of mass M is suspended by a spring of stiffness k. A small block of mass m is placed inside the box. If the system is pulled downward by a distance d and then released from rest:

a.) find the force between the bottom of the box and the block as a function of time;
b.) for what value of d does the block just begin to leave the bottom of the box at the top of the vertical osscilations?

Homework Equations

F(m+M)=mg+ma
x(t)=dcos(ωt)
ω=√(k/(m+M)).

The Attempt at a Solution

I'm unsure of how to proceed to determine the force of reaction from the equations above that I've worked out.

 

[Simon Bridge]

Have a read through:
https://www.physicsforums.com/showthread.php?t=635419