At x₁ = 5 cm,
U₁=1/2×k(x₁)²=1/2×800×0.05²=1J
At x₂=15cm,
U₂=1/2×k(x₂)²=1/2×800×0.15²=9J
W=U₂-U₁=9-1=8J.

In a freely falling lift,
g=0
v=1/2π×√(g/l)=1/2π×√(0/l)=0.

Frequency of driving force is lesser than frequency v of a damped oscillator. The vibrations are nearly in phase with the driving force and response of the oscillator is controlled by spring constant.

In a satellite, g= 0
T=2π√(l/g)=2π√(l/0)=∞.

y=sinωt-cosωt
dy/dt=ωcosωt+ωsinωt
(d² y)/dt² =-ω² sinωt+ω² cosωt
=-ω² (sinωt-cosωt)
a=-ω² y that is a∝y
This satisfies the condition of simple harmonic motion.