The potential energy of a particle of mass 'm' situated in a uni-dimensional potential field varies as U(x)=U₀[1−cosax] where U₀ and a are constants. The time period of small oscillations of the particle about the mean position:
a. 2π(√m/aU₀)
b. 2π(√am/U₀)
c. 2π(√m/a²U₀)
d. 2π(√a²m/U₀)