If a weighted, air-filled balloon sinks in a lake, it will _____.

A. be buoyed up with constant force while sinking

B. probably sink to the bottom and probably rise later

C. sink until it reaches equilibrium and then remain at constant depth

D. always sink to the bottom

E. none of the above

Question

If a weighted, air-filled balloon sinks in a lake, it will _____.

A. be buoyed up with constant force while sinking	

B. probably sink to the bottom and probably rise later	

C. sink until it reaches equilibrium and then remain at constant depth	

D. always sink to the bottom	

E. none of the above

anonymous · Answer

I assume the answer would be E because I just don't see how a full blown helium filled balloon can sink... wouldn't it pop under so much pressure? I doubt it would even sink lower than the surface of the water. I know for a fac that a water balloon floats but I don't see the helium balloon even sitting on top of the water. The balloon with helium always floats upwards while a water balloon pretty much stays  tied to the ground. So how can the balloon filled with helium sink??

theeric · Answer

Hi! The key here is that the balloon is weighted - there is a mass attached to the balloon, giving the balloon+mass system some desnsity.

The "if" tells us one more important thing. The air-filled balloon sinks. I assume it sinks on its own. Also, it's not necessarily helium.

So it will behave like any submerged object that will not float on top.

It will sink until the buoyant force is equal to the force of gravity, if possible.

The balloon+mass could sink to the bottom if the buoyant force is never greater than gravity.

So... We can eliminate two answers.

The prompt has to give you more information to be sure about the other three.

And this seems like "D. always..." looks bad because "always" is not true. Sink to equilibrium is an option at least some of the time. And "E" is appropriate if you make no extra assumptions - A, B, C, and D would be either wrong or not all encompassing.
I'd vote for C!

theeric · Answer

But C assumes a deeper pond or lighter weight.

Maybe go with E, because not all submerged objects get to an equilibrium position. Example, throw a rock into a puddle, or a pool, so you can see it. It's not floating...

anonymous · Answer

Thank you for taking the time to explain.

theeric · Answer

You're welcome! :) Take care!