Science cannot be used to answer questions about Moral judgements
Answer:
man will move in opposite direction with speed

Explanation:
As we know that man is lying on the friction-less surface
so here net force along the surface is zero
so if we take man + stone as a system then net change in momentum of this system will become zero
so here we have


here we have



Velocity is the speed and direction combined.
So, the two jets both are going at the same speed.
But they are going in different directions, so their velocities are different.