Buoyant Force Questions

A buoyant force is nothing but the upward force exerted by water or any other liquid opposite to gravity that makes objects float on their surface. This upward force is also called upthrust. Fluid buoyancy is affected by the density of the fluid, the local acceleration due to gravity, and the fluid’s volume displaced. Any body partially or fully submerged in a fluid appears lighter due to the buoyant force. In water or any other fluid, an object experiences a downward force opposite to the gravitational pull, which reduces the object’s weight when immersed. A fluid’s upward force opposes the weight of an object immersed in it.

Centre of Buoyancy

The centre of buoyancy is the point where the buoyant force is applied or the point on the object where the force acts.

The buoyant force is responsible for floating. In order to float, the object should not be denser than water. If the density of an object is greater than water, it will sink. As a result of buoyancy, human swimmers, fish, ships, and icebergs can stay afloat. The concept of buoyancy is applied to submarines and hot air balloons.

Read More – Buoyant Force

Important Questions with Answers

1. Give an example of buoyant force.

A boat sailing on the river, an iceberg floating on water, a person with a life vest floating on water, a ship floating on the ocean, a helium balloon rising in the air, etc., are examples of buoyant force.

2. Buoyant force depends on_______.

1. the colour of the liquid
2. the density of the liquid
3. the depth of the liquid
4. the weight of the liquid

Answer: B. the density of the liquid

Explanation: Buoyant force of a body depends on the following factors: volume of the body which is submerged in the liquid or volume of the liquid displaced, the density of the liquid and acceleration due to gravity. So here, the answer to this question is the density of the liquid.

3. What causes a buoyant force?

The buoyant force is the upward force acting on an object immersed in a liquid. It is determined by the volume of an object immersed in the liquid and its density. A greater upward pressure caused by water underneath an object causes the buoyant force to increase. We can calculate it by multiplying the mass of water by the weight of the water displaced.

As explained above, buoyancy is caused by the upward pressure of liquid beneath an object.

4. Why is swimming in sea water easier than in freshwater?

Swimming in seawater is easier than swimming in freshwater because seawater contains more salt than river or freshwater; therefore, its density and buoyant force increase, which makes it simpler to swim in seawater.

5. What is Archimedes’ principle?

Archimedes’ principle states that the upward buoyant force exerted on a body immersed in a fluid, whether partially or fully submerged, is equal to the weight of the fluid displaced by the body and acts upward at the centre of mass of the fluid displaced.

6. If a plastic ball floats on the surface of the water on Earth, will it float or sink if placed in a bucket of water on the moon?

The plastic ball will float if placed in a bucket of water on the moon. Since the ball has mass, if it floats on the water on Earth, it experiences an upthrust. The same ball will have the same mass when placed in a bucket of water on the moon, but its weight will decrease (W = mg), and it will experience an upthrust. The upthrust is directly proportional to ‘g’, and ‘g’ is less on the moon (1.63 m/s²), so the ball remains afloat.

7. What happens if the liquid’s buoyant force is equal to, greater than, or less than the weight of the solid object to be immersed in the water?

If the liquid’s buoyant force is equal to a solid object immersed in the water, then the object will remain hung at that depth. If the buoyant force is greater than the weight of the solid object, it will float, and if the buoyant force is less than the object’s weight, it will sink into the liquid.

8. What are the primary forces acting on an object when it is submerged in water?

1. Five
2. Three
3. Two
4. One

Answer: C. Two

Explanation: Two primary forces act on an object when it is immersed in water. A downward force is produced by gravity, whereas an upward force is produced by buoyancy.

9. Which scientist gave an estimate of the buoyant force acting on a solid object submerged in liquid?

1. Sir Issac Newton
2. Archimedes
3. Albert Einstein
4. John Dalton

Answer: B. Archimedes

Explanation: It was Archimedes who determined the magnitude of buoyant force acting on a solid object immersed in liquid.

10. If two objects are submerged, is the buoyant force the same for both the objects?

If both objects are submerged, the buoyant force will be the same unless their density (and therefore weight) is the same. As a result, the upward buoyant force on each object will depend on its density relative to the density of water.

Practice Questions

1. List the factors on which buoyant force depends.
2. Why does an object or solid float or sink in water?
3. How many different types of buoyancy?
4. What happens when the buoyant force equals the gravitational force?
5. Archimedes’ principle describes the magnitude of a buoyant force acting on a body that is partly or completely submerged in a fluid.

A. True

B. False

To learn more about Buoyant Force and Archimedes’ Principle, watch the video below.

Stay tuned to BYJU’S for more exciting questions with solutions. Register for “BYJU’S – The Learning App” as well for a wide variety of interactive, engaging Physics-related videos.