Two particles of mass m each are tied at the ends of a light string of length 2a. The whole system is kept on a frictionless horizontal surface with the string held tight so that each mass is at a distance `a` from the centre P (as shown in the figure). Now, the mid-point of the string is pulled vertically upwards with a small but constant force F. As a result, the particles move towards each other on the surface. The magnitude of acceleration, when the separation between them becomes 2x, is

Options

A. `frac(F)(2m)frac(a)(sqrt(a^2-x^2`
B. `frac(F)(2m)frac(x)(sqrt(a^2-x^2`
C. frac(F)(2m)frac(x)(sqrt(a)`
D. `frac(F)(2m)frac(sqrt(a^2-x^2)(a)`