Question

When a man sitting on a chair tries to lift himself by applying a force on the chair.
A) He cannot lift on the chair.
B) He can lift easily.
C) He can lift himself but very little
D) None of these.

Answer 1

Hint: This is an easy experiment, try pushing the chair on which you are sitting and see if you are able to lift yourself and if you are able to do so, then think about the forces that you are applying to the chair and the forces that are applied by you on the chair.

Complete solution:
When one is sitting on the chair there are no horizontal forces that are being applied, only vertical forces are being applied. The vertical force is: the weight of the body on the chair, the normal force that the chair applies, the weight of the body and the chair on the ground and the upward force applied by the ground on the chair + body. Now, if one pushes the chair i.e. one applies additional force of the arms on the chair there would be a normal force applied by the ground on to that person who is pushing the chair. According to Newton’s third law that every action has an equal and opposite reaction. So, according to the law the ground is applying the same force on the person , so logically the forces are opposite and equal in nature so they should cancel out but this is not so because the forces are applicable on different object, the mass of the earth is very large as compared to the mass of the person so the earth will not move and the person will easily get up.

Final answer option is B. Therefore, when a man sitting on a chair tries to lift himself by applying a force on the chair, he will be able to lift himself easily.

Note: Read the question carefully, in the question the condition is given that the man is applying the force on the chair that means he is pushing the chair and not pulling the chair. Explain the forces that are being applied by the man and the chair on each other.