Given, mass of particle \(=100 g =0.1 kg\) potential energy, \(U=5 x(x-4)\)

\(U=5 x^2-20 x\)

Now, let force be \(F\) :

\(F=-\frac{d U}{d x}=-(10 x-20)\)

Also, \(\quad F=-k x\)

So, \(\quad f=-10(x-2)\).

To simplify, \(\quad f=-10 x\)

So, \(-10 x \)\(=-k x \)\( k \)\(=10 \)

\(k=10\)

So, time period, \(T=2 \pi \sqrt{\frac{m}{r}}\)

\(T=2 \pi \sqrt{\frac{0.1}{10}}\)

\(T=0.2 \pi sec\)