I am puzzled with the following problem.
A man starts to jump. First he will exert force on the floor and he starts accelerating upwards. Then he is off the floor. What is the relationship between the force exerted by him and the force of the floor towards him while he is still on the floor?
My argument is, since the man is still not off the floor, there is no movement at all; as in, his net acceleration towards upwards is zero. Thus, the force of his legs = the force from the floor according to the 3rd law.
However, the problem says that the floor pushes the man upwards with a stronger force than his legs.
To me this is counter intuitive because the floor does not move. I guess I can think of it as that the net force must be upwards because the man can actually jump, but I don't know why this problem is puzzling me so much. Can someone help me out?