Archimedes Principle Questions

Archimedes’ principle states that the buoyant force on an object is the same as the weight of the fluid displaced by the object. Archimedes’ principle is also known as the physical law of buoyancy. According to this law, when an object is completely or partially immersed in a liquid, the apparent loss of weight is the same as the weight of the liquid displaced by it.

Apparent weight= Weight of object (in the air) – Thrust force (buoyancy)

It is given by the formula, Fb = ρ x g x V


Fb – the buoyant force

ρ – the density of the fluid

V – the submerged volume

g – the acceleration due to gravity

The buoyant force is also known as the thrust force, and the formula gives thrust force:

Thrust = ρ x g x V


ρ is the density of the liquid

V is the volume of liquid displaced

Note that if the water displacement weight is less than the object’s weight, the object will sink. The objects will float when the water displacement weight is equal to the object’s weight.

Buoyancy arises from fluid pressure. When the fluid pressure increases along with the depth, this pressure is applied in all directions. Hence, there is an unbalanced upward force on the bottom of a submerged object. Archimedes’ principle is the reason behind the working of the Hydrometer. It is the main principle for the working of a hot-air balloon and the reason behind why submarines are underwater always.

Read more: Archimedes’ Principle

Important Archimedes Principle Questions with Answers

1. What is a hydrometer?

It is a device used for calculating the relative density of liquids.

2. If the weight of the object is more than the weight of the water displaced, the object _____

  1. Remains constant
  2. Floats
  3. Sinks
  4. None of the above options

Answer: c) Sinks

Explanation: When the weight of the displaced water is less than the object’s weight, the object sinks.

3. State true or false: Buoyant force acts in a direction opposite to the gravitational force.

  1. TRUE
  2. FALSE

Answer: a) TRUE

Explanation: The buoyant force always opposes gravitational force.

4. Choose YES or NO: Does the fluid pressure increase with depth.

  1. YES
  2. NO

Answer: a) YES

Explanation: The weight of the fluid applies pressure on the submerged object that increases with depth.

5. Who invented the Archimedes principle?

Archimedes invented the Archimedes principle in the third century BC. Archimedes was a Greek mathematician and physicist.

6. Density is given by the formula _____

  1. Density = Mass+volume
  2. Density = Mass-volume
  3. Density = Mass/volume
  4. Density = Mass*time

Answer: Density = Mass/volume

Explanation: The formula gives density: Density = Mass/volume.

7. Buoyant force is also known as _____.

  1. Stress
  2. Strain
  3. Pressure force
  4. Thrust force

Answer: d) Thrust force

Explanation: Thrust force is also known as the buoyant force.

8. Thrust force is given by the formula _____

  1. \(\begin{array}{l}\rho *V*g\end{array} \)
  2. \(\begin{array}{l}\rho +V+g\end{array} \)
  3. \(\begin{array}{l}\rho *V/g\end{array} \)
  4. \(\begin{array}{l}\rho +V*g\end{array} \)

Answer: a)

\(\begin{array}{l}\rho *V*g\end{array} \)

Explanation: Thrust force is given by the formula

\(\begin{array}{l}\rho *V*g\end{array} \)

9. Archimedes’ principle helps to calculate the buoyancy of any floating object that is _____ immersed in a fluid

  1. Only partially
  2. Only completly
  3. Neither partially nor completely
  4. Both partially and completely

Answer: d) Both partially and completely.

Explanation: Both partially and completely immersed buoyancy of any floating object can be calculated.

10. When does the object float?

The object will float when the weight of the water is displaced equal to the weight of the object.

Practice Questions

  1. State Archimedes principle.
  2. What is Archimedes’ principle also known as?
  3. Give examples where Archimedes’ principle is applied?
  4. What is thrust force?
  5. How is the Archimedes principle mathematical written?

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