A monkey pulls the midpoint of a 10 cm long light inextensible string connecting two identical objects A and B lying on smooth table of masses 0.3 kg continuously along the perpendicular bisector of line joining the masses. The masses are found to approach each other at a relative acceleration of 5 ms−2 when they are 6 cm apart. The constant force applied by monkey is
a. 4 N
b. 2 N
c. 3 N
d. None of these