Answer:
0.72 Hz minimum frequency
Explanation:
When the damping is negligible,Amplitude is given as

here
= (6.30)/(0.135) = 46.67 N/m kg
= 1.70/(0.135)(0.480) = 26.2 N/m kg
From the above equation , rearranging for ω,

⇒ ω² =46.67 ± 26.2 = 72.87 or 20.47
⇒ ω = 8.53 or 4.52 rad/s
Frequency = f
ω=2 π f
⇒ f = ω / 2π = 8.53 /6.28 or 4.52 / 6.28 = 1.36 Hz or 0.72 Hz
The lower frequency is 0.72 Hz and higher is 1.36 Hz