question_answer

  Akhtar, Kiran and Rahul were riding in a motor car that was moving with a high velocity on an expressway when an insect hit the windshield and got struck on the windscreen. Akhtar and Kiran started pondering over the situation. Kiran suggested that the insect suffered a greater change in momentum as compared to the change in momentum of the motor car (because the change in velocity of the insect was much more than that of motor car). Akhtar said that since the motor car was moving with a larger velocity, it exerted a larger force on the insect; and as a result the insect died. Rahul while pulling on a new explanation that the both the motor car and the insect experienced the same force and a change in their momentum. Comment on these suggestions.                              [NCERT]

Answer:

                  Kiran's suggestion is wrong because the mass of insect is very small and velocity of insect will be same as that of motor car after collision; hence change in momentum of insect cannot be greater than that of a motor car. Akhtar's statement is also wrong; because the force is not due to larger velocity, it is due to change in momentum. Rahul's suggestion is correct; because there is no external force on the system comprising insect and motor car; net momentum of system is conserved in the collision; hence i.e., change in momentum of insect and motor car are equal and opposite. Moreover, the action force exerted by insect on motor car must be equal to reaction force exerted by motor car on insect.