Question

Assertion (A) : A man standing on a completely frictionless surface can propel himself by whistling. 

Reason (R) : If no external force acts on a system, its momentum cannot change.  

Codes: 

(a) Both A and R are true and R is the correct explanation of A 

(b) Both A and R are true but R is not a correct explanation of A 

(c) A is true but R is false 

(d) A is false but R is true

Answer 1

(b) First statement can be explained on the basis of laws of motion. First statement involves the use of Newton's third law of motion, "For every action there is an equal and opposite reaction". In first case while whistling a man uses his breathe as a propellant to propel himself. The second statement can be explained on the basis of law of conservation of linear momentum according to which the momentum of body remains conserved until any external force acts upon it.