# Buoyancy Problem Involving Archimede's Principle

• aokidopi
In summary, the wooden ball with a weight of 14.0 N is suspended in water and at rest, with exactly 50% of its volume submerged. The spring scale reads 5.00 N. Using a density of water of 1000 kg/m3 and g = 10.0 m/s2, the following questions are addressed: (a) If the ball was only 20.0% submerged in water, the spring scale would read 3.6 N. (b) The density of the ball is 200 kg/m3. (c) The volume of the ball is 0.0018 cubic meters. The solution was found by applying Newton's second law and Archimede's principle.
aokidopi
1. A wooden ball with a weight of 14.0 N hangs from a string tied to a spring scale. When the ball is at rest, exactly 50% submerged in water, the spring scale reads 5.00 N. For this problem, we will use a density of water of 1000 kg/m3, and we will use g = 10.0 m/s2.

(a) If the ball was only 20.0% submerged in water instead, what would the spring scale read?
(b) Determine the density of the ball.
(c) Determine the volume of the ball.

2. Archimede's Principle

3. I was able to find the answer to part A by applying Newton's second law on the forces acting on the wooden ball. Using the buoyant force from the given and the percentage of submergence, I set a proportion finding the buoyant force for the new percentage of submergence and resulted in 3.6 N. Since the scale measures the tension in the spring, tension would be mg-buoyant force.

However, I am having troubles with part b and c. Using Archimede's principle of buoyant force = density of fluid * volume displaced* g, I resulted in volume displaced of 3.6 E-4 cubic meters. Using a derivative of the equation, density of fluid*volume displaced=density of object*volume of object, I set the volume displaced/volume of object as 0.2, since that is the percentage of the object submerged and resulted in a object volume of 0.0018 cubic meters. Using this proportion of 0.2 as equal to density of object/density of fluid, I resulted in a object density of 200 kg/cubic meters. However, these answers were incorrect.

Answer part c first: When the ball is first submerged 50% you are essentially given the weight of the water displaced. What volume of water is that? What then is the volume of the ball?

You have the weight of the ball, thus its mass. You now have the volume too. So what's the density of the ball?

gneill has the right idea.

P.S. aokidopi - you got part (a) correct.

Got it, thanks!

I'm a little confused still. So at 50% immersion, the force of tension is 5 N, so the F_B must be 9 N to add up to the total 14 N.
9 N / 10 m/s^2 is 0.9 kg of total displaced water.
Where do I go from here?

That's right so far, sickboy. We also know the density of the water, so it is simple to find the volume of water displaced.

And from there, you know the volume of water displaced is half of the volume of the ball, so this gives you the volume of the ball.

So V=m/d, and because that is the volume at 50% submerged, it should be multiplied by 2?

exactamundo. (yes)

## 1. What is Archimedes' Principle?

Archimedes' Principle is a scientific law that states that the buoyant force experienced by an object immersed in a fluid is equal to the weight of the fluid that the object displaces. This principle helps to explain why objects float or sink in liquids.

## 2. How does Archimedes' Principle relate to buoyancy?

Archimedes' Principle is the fundamental principle behind buoyancy. It explains why objects float or sink in a fluid and is used to calculate the buoyant force on an object. This principle is based on the fact that the pressure exerted by a fluid on an object is greater at the bottom than at the top, resulting in a net upward force on the object.

## 3. What factors affect buoyancy in a fluid?

The buoyant force experienced by an object in a fluid is affected by several factors, including the density of the fluid, the volume of the object, and the acceleration due to gravity. The shape and size of the object also play a role in determining its buoyancy.

## 4. How can Archimedes' Principle be applied in real life?

Archimedes' Principle has many practical applications in everyday life. It is used in designing ships and submarines, determining the appropriate buoyancy of objects such as life jackets and buoys, and even in determining the body fat percentage of a person using underwater weighing techniques.

## 5. Can Archimedes' Principle be used for objects in air?

While Archimedes' Principle is often associated with objects in fluids, it can also be applied to objects in air. This is because air is considered a fluid, and the same principles of buoyancy apply. For example, hot air balloons use Archimedes' Principle to stay afloat in the air.

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