Conservation of momentum is valid here?

[Mohammed Shoaib]

Question says" When a car comes to a normal stop its momentum is not conserved. Does this violate the principle of conservation of momentum? Explain. What happens to the car's kinetic energy?"

My question is why momentum is not conserved when a car comes to a normal stop?

 

[Orodruin]

What is the momentum before and what is the momentum after the stop?

 

[Mohammed Shoaib]

Before stop the momentum is decreasing and after the stop it is zero.

 

[Mohammed Shoaib]

Then what about the principle of conservation of momentum?

 

[Orodruin]

Yes, what about it? What are your thoughts?

 

[Mohammed Shoaib]

Momentum is conserved when no external force acts on the system. When the car comes to normal stop, the external force from the road or from the brake acts on the car to stop. Hence, the conservation of principle is not valid in this process. Am I right.

 

[Mohammed Shoaib]

And the kinetic energy of the car is lost as heat to the car and the surrounding.

 

[Orodruin]

Momentum is conserved when no external force acts on the system. When the car comes to normal stop, the external force from the road or from the brake acts on the car to stop. Hence, the conservation of principle is not valid in this process. Am I right.

And if you consider the entire car-earth system?

 

[Mohammed Shoaib]

Then momentum is conserved. Is it not?

 

[Khashishi]

It sounds like you got it.

 

[Orodruin]

Then momentum is conserved. Is it not?

Yes, it should be. Yet the car momentum after is zero and the one before non zero.

This is a conundrum for many people who are just learning conservation of momentum.

 

[Mohammed Shoaib]

Yes, it should be. Yet the car momentum after is zero and the one before non zero.

This is a conundrum for many people who are just learning conservation of momentum.

Thanks for your kind help.