Aamc 9 # 25

[typicalindian]

"Assume that a pan of "dry water" is momentarily disturbed. Which of the following concepts best explains why the resulting sloshing oscillations persist for a fairly long time"

A. Conservation of energy
B. Conservation of momentum

The answer is A but I picked B. Can someone please explain why B is wrong?

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[folktale]

I was actually thinking between those two as well. I picked momentum conservation at first as well, but I marked the question. Then I went back to this question after I finished everything and switched it to energy conservation at the last second. I just thought about the height difference of the water, going up then down. It reminded me of a spring oscillation. So I decided PE=KE.

 

[typicalindian]

hmm I think I may have reasoned it out. Conservation of momentum just says that "an object in motion will stay in motion unless there is a force acting on it" Since velocity is changing as the oscillations occur doesn't that mean that momentum is actually not being conserved? Where as the total energy of the system is conserved where the energy is just converting between KE and PE. Is my reasoning right, or am I completely off target?

 

[folktale]

Momentum is conserved in collisions. I am not sure if it is conserved in harmonic motions like oscillations.

 

[typicalindian]

Momentum is conserved in collisions. I am not sure if it is conserved in harmonic motions like oscillations.

right right that was my point.