Does placing something in water affect the water's weight?

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Homework Help Overview

The discussion revolves around the effects of placing objects in water on the overall weight of a system, specifically in the context of a fire truck carrying firefighters and a tank of water. Participants explore the implications of mass and buoyancy in relation to weight changes.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants question whether the mass of a system changes when components are rearranged, such as moving firefighters into a water tank. They explore the relationship between buoyancy and weight, considering how forces interact in different scenarios.

Discussion Status

The discussion is ongoing, with participants examining various interpretations of mass and weight in the context of buoyancy. Some guidance has been offered regarding the balance of forces, but no consensus has been reached on the implications for the overall weight of the system.

Contextual Notes

Participants are grappling with the assumptions surrounding mass and buoyancy, particularly in relation to the specific setup of the problem involving a fire truck and firefighters. There is an underlying uncertainty about how these factors influence the total weight of the system.

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"A fire truck carrying a load of fire fighters and a large tank of water is about to cross a bridge that may not support the load. The chief suggests that some of the fire fighters get into the tank so the load will be less. Is this a good idea? Explain."

I have no idea where to begin. I know that the fire fighters will displace a volume of water equal to their own, but I don't know if that would change the weight of the whole system. Any help or leads would be appreciated.
 
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The weight of the system depends on the total mass of the system. By placing firefighters in the tank, does its mass change?
 
Does the mass of something change when you rearrange its components? If you move a book from the side pocket of your backpack to the main pocket, is the backpack going to get lighter/heavier?
 
No... the mass of the system doesn't change. That's what I initially thought, but then I proceeded to confuse myself by trying to reason that if something were suspended in a liquid, the liquid exerts an upward buoyant force that balances out the downward force of gravity. If the downward force of gravity (the weight) of one of the objects is being balanced out, won't the weight of the system change?
 
When the firefighter was sitting on his seat, his weight was balanced out by the normal force of the seat. If he goes into the tank, it'll be balanced out by buoyancy.
 
Your logic is sound. Thanks for the help!
 

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