A $1 \mathrm{~kg} mass is suspended from the ceiling by a rope of length 4 \mathrm{~m}. A horizontal force 'F' is applied at the mid point of the rope so that the rope makes an angle of 45^{\circ} with respect to the vertical axis as shown in figure. The magnitude of F is :
(Assume that the system is in equilibrium and g=10 \mathrm{~m} / \mathrm{s}^2$)