Question:
A particle of mass m moves in the xy plane with potential energy U(x,y)=kxy/2. If the particle begins at the origin, then it is possible to displace it slightly in some direction, so that the particle subsequently oscillates periodically. What is the period of this motion?
(A) 2πm/4k.
(B) 2πm/2k.
(C) 2πm/k.
(D) 2π2m/k.
(E) 2π4m/k.