A) He cannot lift on the chair
B) He can lift easily
C) He can lift himself but very little
D) None of the above
Correct Answer: A
Solution :
Here the person should be imagined to be sitting with his legs folded on the chair i.e., the person should be imagined to be contained in the chair i.e., the chair and the person form one system (or one body). Therefore, the action and reaction forces should be imagined to act simultaneously on the single body the person and the chair constitute. Therefore, they cancel each other. Thus in all those situations where action and reaction act on the same body (or system) they become balanced making action ineffective. If you try to lift yourself by applying downwards push on the chair by hands you can succeed in lifting yourself a little bit but you cannot separate yourself (even hands should leave the contact) from the chair even for a moment. Thus the person cannot lift himself by applying force on the chair. For the same reason when air is blown on a sail attached to a boat from an electric fan placed on the boat, the boat does not move. It is so because the blown air strike the sail (action) and tries to move the boat forward. Same air pushes the fan backwards (reaction). As the fan is contained in the boat, the boat and the fan from one system, the boat does not move. Similarly, passengers inside a stationary compartment cannot make to move it by pushing it from inside because the passengers are contained in the compartment.
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