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

According to the law of conservation of momentum:

Momentum of the car and insect system before collision = Momentum of the car and insect system after collision

Hence, the change in momentum of the car and insect system is zero.

• Kiran's fallacy is that the magnitude of change in momentum of the insect is much greater than the magnitude of change in momentum of the car. His argument is wrong. The velocity of the car was very high; basically, the car applied a lot of force on the insect, Akhtar's argument is also wrong.
• Rahul's argument is correct. Equal force is applied to both because reaction is opposite to action. Also, the magnitude of change in momentum is also the same, while momentum is conserved during collision.
• Akhtar made a correct conclusion because the mass of the car is very large as compared to the mass of the insect.