Need help with determining acceleration when given a distance

JDM5000

1. The problem statement, all variables and given/known data
A machine has a steel shuttle with mass m that is pulled along a vertically positioned square steel rail by a spring with a spring constant k. The shuttle is released when the spring acts on the shuttle with force equal to F at a 45 degree angle.
a) what is the initial acceleration of the shuttle?
b) what will be the acceleration of the shuttle after it moved a distance L?



2. Relevant equations

F=ma ; X=vt+(1/2)at^2 ; u_k(n)=f_k ;


3. The attempt at a solution
For A
Ʃx= K*cos(45)-f_k=m_x*a
Ʃy=K*sin(45)+N-mg=0

a= (kcos45-uk(mg-Ksin45))/m
a= (t/m)(kcos45-ksin45)(uk*g)

For B)
Wouldn't it just be my a_1 subtracted by the new value of a?
I was thinking since theta is going to change with the elastic band.