First, Mass x Velocity is Momentum, not Force. Mass x Acceleration is Force.
The issue is that the kinetic energy is not just expended by striking a target and cutting into it, it is also expended countering air friction (which gets higher the faster something goes) and twisting and turning in the air. Also, with a low mass comes very low inertia, which means it will slow down very quickly. The low mass also means when it hits it will decelerate almost instantly before it can cut very deep.
A monofilament whip or grenade uses a super-thin carbon nanotube wire which has a Density of 1.33-1.40 g/cm3; and a Diameter of 1.2nm, for an approximate Volume of 0.00000113cm3 per meter length. That gives a 3m long strand a total Mass of 0.0000034g (rounded up).
Assuming it is travelling at roughly the speed of sound, 340m/s, and ignoring air friction, that gives each strand (0.5*0.0000034g*(340m/s)2=) 0.197Joules of kinetic energy. At twice the speed of sound, it is still only 0.79J.
That isn't enough for even monowire to cut through or even into much of anything. Even hitting bare flesh it would be unlikely to do anything but superficial scratches. The biggest danger would be getting tagged with the end of one of the threads as it whizzed past you or getting hit in the eye, but even a cheap plastic lens would protect you from that.
And then you take into account deceleration due to wind resistance and the difficulty of accelerating something that light to a reasonable speed in the first place without an explosion that does more damage than the wires and you have a weapon that simply shouldn't work, not due to technological limitations but due to elementary physics. I wouldn't allow it in my game, because it is simply too unrealistic and breaks suspension of disbelief.