Basic Buoyant Force HW Question

In summary, the equation for buoyant force is Fb = (density)(volume)(acc. due to gravity). To find volume, use the equation for buoyant force and solve for V.
  • #1
5.0stang
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[SOLVED] Basic Buoyant Force HW Question

First time doing this, so bare with me:)

Homework Statement



A 53kg girl dives off a raft 4m square floating in a freshwater lake. By how much does the raft rise?

Density of water = 1000kg/m^3

Use the equation for buoyant force. Then solve the equation for V.

Of course, volume = L x W x H.

g = 9.8 m/s^2

Fb = weight of girl in Newtons


The Attempt at a Solution



My teacher gives us the equation for buoyant force as Fb = (density)(volume)(acc.due to gravity).

The answer is to be given in cms (centimeters).

Fb = (1000)(?)(9.8)

I am trying to get the volume, knowing that there is 4m squared. I am just missing the height.

Thanks for any ideas...
 
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  • #2
Okay, just looking over my notes one more time. My teacher said to use the weight of the girl (53kg) to equal Fb.

How do I convert 53kg to Newtons? I can use online calculators, but that is not helping me learn. It looks like it is 9.8 x 53 = 519.4 Newtons

So I should be getting Fb = (1000)(V)(9.8) or 519.4 = (1000)(V)(9.8).

I just have to solve for V it looks like.
 
Last edited:
  • #3
I am trying to solve for volume. I have 4m ^2 given in the problem.

Okay, the formula to work from is:

1. Fb = (Density in kg/m^3)(Volume)(Acc. Due to Gravity)
2. 519.4 = (1000 kg/m^3)(V)(9.8 m/s^2)
3. 519.4 = 9800V
4. Volume = 18.87 (units?)

Is this correct so far?

How do I convert this to centimeters.?
 
  • #4
5.0stang said:
I am trying to solve for volume. I have 4m ^2 given in the problem.

Okay, the formula to work from is:

1. Fb = (Density in kg/m^3)(Volume)(Acc. Due to Gravity)
2. 519.4 = (1000 kg/m^3)(V)(9.8 m/s^2)
3. 519.4 = 9800V
4. Volume = 18.87 (units?)

Is this correct so far?

How do I convert this to centimeters.?

How do you get 4 from 3?

Are you able to understand the concept behind what you are doing? Refer to this similar problem in PF and see.

https://www.physicsforums.com/showthread.php?t=214070
 
  • #5
Sorry for the late response. I figured out the problem.

The professor made a typo in our question, and she corrected it. I solved it very quickly after that.

Thanks anyways!
 
  • #6
Last edited by a moderator:

1. What is buoyant force?

Buoyant force is the upward force exerted by a fluid on an object immersed in it. It is equal to the weight of the fluid that the object displaces.

2. How is buoyant force calculated?

Buoyant force is calculated using the formula Fb = ρVg, where Fb is the buoyant force, ρ is the density of the fluid, V is the volume of the displaced fluid, and g is the acceleration due to gravity.

3. What factors affect the buoyant force on an object?

The buoyant force on an object is affected by the density of the fluid, the volume of the displaced fluid, and the acceleration due to gravity. It is also affected by the shape and size of the object.

4. How does buoyant force relate to Archimedes' principle?

Archimedes' principle states that the buoyant force on an object is equal to the weight of the fluid that the object displaces. This means that an object will float if its weight is less than the weight of the fluid it displaces, and it will sink if its weight is greater than the weight of the displaced fluid.

5. Can buoyant force be negative?

No, buoyant force cannot be negative. It is always directed upwards, and if the object is denser than the fluid, the buoyant force will be less than the weight of the object and it will sink. However, the net force on the object will still be positive, as there will be a downward force due to gravity.

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