Question

Akhtar, Kiran and Rahul were riding in a motorocar 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.

The insect gets stuck on the windscreen. This means that the direction of the insect is

reversed. As a result, the velocity of the insect changes to a great amount. On the other hand,

the car continues moving with a constant velocity. Hence, Kiran’s suggestion that the insect

suffers a greater change in momentum as compared to the car is correct. The momentum of

the insect after collision becomes very high because the car is moving at a high speed.

Therefore, the momentum gained by the insect is equal to the momentum lost by the car.

Akhtar made a correct conclusion because the mass of the car is very large as compared to

the mass of the insect.

Rahul gave a correct explanation as both the car and the insect experienced equal forces

caused by the Newton’s action-reaction law. But, he made an incorrect statement as the

system suffers a change in momentum because the momentum before the collision is equal to

the momentum after the collision.