if a room is closed for 2-4 hours then when we open the door we need a little bit of more energy than the actual energy and feel someone is pushing the door from the back side . what is the reason behind it ? which force is that?

The reason is because the pressure of the air inside the room drops with time which makes opening the door to require an increased amount of force to make up for the reduced pressure inside the room

Explanation:

From the kinetic theory of gases we have the following relation;

Where:

K = Boltzmann constant

T = Temperature

m = Mass

MW = Molecular weight

V = Volume

= Root mean square velocity

Whereby the room door is closed, the kinetic energy of the air particles will be used up such that the average velocity of the particles will decrease, given that the volume of the room is constant, the pressure inside the room will drop below the original pressure outside the room such that the force on the door due to the outside pressure is larger than the force on the door from inside the room requiring a larger amount of force to overcome the resistance of the now higher outside pressure force.

1/0.14nm = 10^10/1.4 a lot

seeing the graph would