What is the weight of a hollow sphere underwater?

In summary, To find the weight of the hollow sphere under water, you need to calculate the net force of its weight and buoyancy. The average density of the sphere is 3 g/cm^3 and its mass is 120g. After converting to SI units, the weight on land is found to be 0.12N. To calculate the buoyant force, you need to use the density of water and the volume of water displaced, which is equal to the volume of the sphere. This results in a weight of 0.8N underwater.
  • #1
test2morrow
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Homework Statement



A hollow sphere has average density of 3 g/cm^3 and a mass of 120g. What will the sphere weight under water?

correct answer: 0.8

Homework Equations



d=m/v

w=mg


The Attempt at a Solution



I converted 120g into kg and then used w=mg to find weight on land. however, this does get 0.8N underwater. Please help thanks!
 
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  • #2
first, change all the units to SI units, giving you:
3000 kg/m3 for the sphere's density
0.12 kg for its mass

to possibly calculate the sphere's weight underwater, you must calculate the net force of the sphere's weight downwards and buoyancy upwards

buoyant force is equal to the weight of the water displaced by the ball, thus you calculate the weight by using the mass of the water displaced, found by:
1. density of water
2. the volume of water displaced, which is equal to the volume of the sphere since it is fully submerged
 
  • #3
got it, thanks!
 

1) What is the weight of a sphere underwater?

The weight of a sphere underwater depends on its size, density, and the depth at which it is submerged. The weight can be calculated using the formula W = ρVg, where W is the weight, ρ is the density of the fluid, V is the volume of the sphere, and g is the acceleration due to gravity.

2) Does the weight of a sphere change when it is underwater?

Yes, the weight of a sphere changes when it is underwater due to the buoyant force acting on it. The buoyant force is equal to the weight of the fluid displaced by the sphere, and it counteracts the weight of the sphere, making it appear lighter.

3) Why does a sphere feel lighter when it is submerged in water?

A sphere feels lighter when it is submerged in water because of the buoyant force. This force is caused by the pressure difference between the top and bottom of the sphere. The pressure at the bottom is higher, and this upward pressure reduces the apparent weight of the sphere.

4) How does the weight of a sphere change as it goes deeper underwater?

The weight of a sphere increases as it goes deeper underwater due to the increased pressure. The deeper the sphere is submerged, the greater the pressure acting on it, which increases its weight. However, the buoyant force also increases with depth, so the net effect on the weight may vary.

5) Can the weight of a sphere underwater be negative?

No, the weight of a sphere underwater cannot be negative. Weight is a measure of the force of gravity acting on an object, and it is always positive. However, the buoyant force can be greater than the weight of the sphere, making it appear to have a negative weight. This is known as negative buoyancy.

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