In a, high-speed head-on collision between a subcompact car (mass around 1000 kg

Question

In a, high-speed head-on collision between a subcompact car (mass around 1000 kg) and a semi-truck (mass around 36,000 kg), the subcompact car is usually crushed while the semi-truck sustains much less damage. This usually results in the driver of the subcompact car being killed instantly in the crash, while the driver of the semi-truck may escape with only minor injuries. Many might attribute the drastically different injury levels to a matter of change in momentum: The semi-truck only slows down a little bit after the collision while the subcompact car is forcibly pushed backwards by the semi-truck after the collision. It therefore seems like the subcompact car experiences a violent shift in momentum while the semi-truck barely experiences any change at all. Explain in words (a) why the change in momentum cannot be the reason for the subcompact car being crushed while the semi-truck is not, and (b) what is responsible for this difference. Support your argument using physical principle (e.g. Newton's laws, Work-Kinetic Energy theorem, etc.).

Explanation / Answer

a)

According to the law of conservation of linear momentum the momentum of the bodies before collision is equal to the momentum of the bodies after collision. Hence the momentum (force) experienced by the drivers of both subcompact car and semi truck is same before and after collision. Hence the change in momentum is not a reason to the more impact on the subcompact car and less impact on the semi truck.

b)

Here the responcible factor for the hevy damage of subcompact car is the huge change in the acceleration of it. In case of the semi truck, there no much change in velocity or acceleration after the collision this implies the less damage for the semi truck. But in case of subcompact car there is huge change in velocity and as well as the acceleration after the collision. This is only the cause of the damage of the subcompact car.

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