Calculating Impulse Ratio for Colliding Molecules A and B

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SUMMARY

The discussion focuses on calculating the impulse ratio for two identical molecules, A and B, colliding with a vertical wall at a 20-degree angle. Molecule A rebounds with the same speed, resulting in an impulse of 2Mvcos20, while molecule B sticks to the wall, leading to an impulse of Mvcos20. The key distinction lies in the momentum change: A's momentum is reflected, while B's momentum is completely absorbed by the wall. Thus, the impulse experienced by A is twice that of B, establishing the ratio of impulse A to B as 2:1.

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Fuzzykatecake
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Two identical molecules A and B each of mass M travel with the same velocity towards a vertical wall at an angel 20 degrees with respect to the normal to the wall. A rebounds from the wall with the same speed while B sticks to the wall.

Determine the ratio of the implus experience by A to that by B during collision.

I know the inpluse experienced by A is
final momentum - initial momentum=
Mvcos20-(-mvcos20)

But for B, why is the impluse mv? And not 0- mvcos20
 
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What is the velocity of B before the collision? What is the velocity after? As a result, what is the difference in B's momentum before and after?
 
Orodruin said:
What is the velocity of B before the collision? What is the velocity after? As a result, what is the difference in B's momentum before and after?
Isn't the velocity of B before collision vcos20. And velocity after is 0 since is stick to wall. Therefore the momentum is 0-mvcos20.
But the correct answer is mv which I don't understand why
 
Fuzzykatecake said:
Isn't the velocity of B before collision vcos20.
No, that is the velocity component orthogonal to the wall.
 
Orodruin said:
No, that is the velocity component orthogonal to the wall.
But why for A is vcos20, what's the difference?
 
Fuzzykatecake said:
But why for A is vcos20, what's the difference?
A does not stick to the wall. The momentum component of A orthogonal to the wall is simply reflected while that perpendicular to it is unchanged.
 

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