Answer:
Step-by-step explanation:
force constant of spring k = force / extension 
= 35.6 / 0.5 
k = 71.2 N / m 
angular frequency ω of oscillation by spring mass system 

where m is mass of the body attached with spring 
Putting the values 

ω = 3.77 radian / s 
The oscillation of the mass will be like SHM having amplitude of 0.5 m and angular frequency of 3.77 radian /s . Initial phase will be π / 2 
so the equation for displacement from equilibrium position that is middle point can be given as follows 
x = .5 sin ( ω t + π / 2 )
= 0.5 cos ω t 
= 0.5 cos 3.77 t .
x = 0.5 cos 3.77 t .