Question

Akhtar, Kiran and Rahul were riding in a motorcar that was moving with a high velocity on an expressway when an insect hit the windshield and got stuck 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 motorcar(because the change in the velocity of the insect was much more than that of the motorcar). Akhtar said that since the motorcar was moving with a larger velocity, it exerted a larger force on the insect. And as a result the insect died. Rahul while putting an entirely new explanation said that both the motorcar and the insect experienced the same force and a change in their momentum. Comment on these suggestions.

Answer 1

Kiran's statement:

Change in momentum of the insect and the motorcar is equal by conservation of momentum. The velocity of insect changes significantly because its mass is very small compared to the motorcar. Similarly, the velocity of motorcar is very insignificant because its mass is very large compared to the insect. Hence, Kiran's statement is false.

Akhtar's statement:

By newton's third law of motion, action and reaction force are equal and opposite and they act on different bodies. Hence, the motorcar and insect both experience the same force. Since the mass of the insect is very small compared to the motorcar, it suffers a huge change of velocity as compared to the car. Due to this, insect dies. Hence, Akhtar's statement is false.

Rahul's Statement:

As discussed before, both the motorcar and the insect experience the same force and change in momentum. Hence, Rahul's statement is correct.