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.
Answers
The idea that was put forward by Kiran that the insect would have had suffered a greater change in momentum when compared to the change in momentum of motor car is completely wrong.
Whereas the suggestion made by Akhtar that motor car had exerted a larger force on the insect because of the large velocity of motor car is equally wrong.
Thus it is the explanation put forward by Rahul which is absolutely correct.
Answer:
As per the law of conservation of momentum, the total momentum before the collision between the
insect and the car is equal to the total momentum after the collision. Therefore, the change in the
momentum of the insect is much greater than the change in momentum of the car (since force is
proportional to mass).
Akhtar’s assumption is partially right. Since the mass of the car is very high, the force exerted on the
insect during the collision is also very high.
Kiran’s statement is false. The change in momentum of the insect and the motorcar is equal by
conservation of momentum. The velocity of insect changes accordingly due to its mass as it 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.
Rahul’s statement is completely right. As per the third law of motion, the force exerted by the insect on
the car is equal and opposite to the force exerted by the car on the insect. However, Rahul’s suggestion
that the change in the momentum is the same contradicts the law of conservation of momentum.
Explanation:
Rahul’s statement is completely right.