Answer:
x=0.5 sin 4 t
Step-by-step explanation:
Given that:
mass m = 4 kg
Stiffness K =64 N/m
Given spring mass system will be in simple harmonic motion.We know that in simple harmonic motion the natural frequency given as follows

Now by putting the values

The equation of SHM given as

The solution of above equation will be

x=A sin 4 t
Given at t=0 ,V= 2 m/s
So
V= 4 A cos 4 t
2 = 4 A
A= 0.5
The equation of motion will be
x=0.5 sin 4 t