Buoyancy Problem Help: Understanding Changes in Water Level and Scale Readings

  • Thread starter ductape
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In summary: Check the red ones. On a first read, I think they all have different answers from the ones you chose and from each other.hmm...
  • #1
ductape
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Fill in the blanks with:
A) increases B)decreases C) less than D) greater than E) stays the same F)stays the same as

i) A block of wood floats in a pail of water in a stationary elevator. The level of water in the pail _____ when the elevator accelerates downward.

ii) Two identical shallow containers are placed on identical scales. A live duck is put in one container. Both containers are then filled with water to their brims; it is observed that the duck is standing on the bottom of its container. The reading on the scale under the container with the ducks is _____ the reading on the other scale.

iii) A boat containing a cement block floats in a swimming pool. The water level in the pool ___ when the block is thrown to shore.

iv) A boat containing a cement block floats in a swimming pool. The water level in the pool ___ when the block is dropped into the water.

v) Two balloons of the same volume are fulled with helium and hydroge, respectivley. The buoyant force on the helium filled balloon is ______ the buoyant force on the hydrogen filled balloon.


I said ADABC but that is not correct. I am fairly sure of iii, iv, and v.
ii i am not sure what aspects to consider, and for i I cannot decide if it would stay the same or rise.
Thanks for any help!
 
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  • #2
ductape said:
I said ADABC but that is not correct. I am fairly sure of iii, iv, and v.
ii i am not sure what aspects to consider, and for i I cannot decide if it would stay the same or rise.
Thanks for any help!

Check the red ones. On a first read, I think they all have different answers from the ones you chose and from each other.
 
  • #3
hmm...
For iii) i am thinking B
for v) hydrogen is less dense than helium so wudnt it push up with a greater force? I am kinda confused about that one.
for i) i really cannot seem to get my reasoning straight, wouldn't it have a greater weight if it was going downwards, displacing more water? But on the other hand its density relative to water wouldn't change...
 
  • #4
ductape said:
hmm...
For iii) i am thinking B
for v) hydrogen is less dense than helium so wudnt it push up with a greater force? I am kinda confused about that one.
for i) i really cannot seem to get my reasoning straight, wouldn't it have a greater weight if it was going downwards, displacing more water? But on the other hand its density relative to water wouldn't change...

For iii) when the block is in the boat it is displacing its own weight of water. When it is thrown out, that water is no longer dispalaced. Less displaced water means lower level. I think you've got it

For v) you are being asked for the buoyant force. What determines the buoyant force?

For i) how does water pressure increase with depth? Neglecting evaporation, what would happen if you took the pail and block to the moon? How does that compare to the situation in the elevator. You have the key in your quote.
 
  • #5
ok so for i) i am now thinking E
and for v) i am thinking d
 
  • #6
does that sound ok?
 
  • #7
although research on the net seems to indicate that helium is less buoyant than hydrogen
 
  • #8
Just got the right answer.
It was EDBBF
i forgot the exact definition of buoyant force.
Thank you so much!
 

1. What is buoyancy?

Buoyancy is the upward force that is exerted by a fluid, such as water or air, on an object that is submerged or floating in the fluid.

2. How is buoyancy calculated?

Buoyancy is calculated using Archimedes' principle, which states that the buoyant force on an object is equal to the weight of the fluid that the object displaces. This can be expressed as Fbuoy = ρVg, where ρ is the density of the fluid, V is the volume of the object, and g is the acceleration due to gravity.

3. What factors affect buoyancy?

The factors that affect buoyancy include the density of the fluid, the volume of the object, and the acceleration due to gravity. Additionally, the shape and weight distribution of the object can also impact its buoyancy.

4. How does buoyancy help objects float?

When an object is placed in a fluid, the fluid exerts an upward force on the object, which is greater than the force of gravity pulling the object downward. This results in a net upward force, allowing the object to float.

5. How can buoyancy be used to solve problems?

Buoyancy can be used to solve problems related to floating and sinking of objects in different fluids. It can also be used to calculate the weight and volume of an object by measuring its buoyant force in a fluid with known density. Additionally, understanding buoyancy can help in designing and constructing objects that need to float or maintain a specific position in a fluid.

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