As the bubble moves upwards, besides the buoyancy force the following forces are acting on it- AOnly the force of gravity
- BThe force due to gravity and the force due to the pressure of the liquid
- CThe force due to gravity, the force due to the pressure of the liquid and the force due to viscosity of the liquid
- DThe force due to gravity and the force due to viscosity of the liquid
View written solutionFree
Correct answer: D
- Identify all external forces on the bubble
A gas bubble moving upward in a liquid can experience:
- Buoyant force upward due to pressure difference in the liquid
- Weight (gravity) of the gas inside the bubble downward
- Viscous drag due to relative motion between bubble and liquid, opposite to motion
- Pressure forces exerted by the surrounding liquid on the bubble surface
The question says: "besides the buoyancy force", which means we should list other forces apart from buoyancy.
- Understand the role of pressure force
The liquid exerts pressure on the bubble from all sides. If we consider the net effect of all these pressure forces over the bubble surface, their resultant is exactly the buoyant force.
So, the net force due to liquid pressure is not something additional to buoyancy. It is already accounted for as buoyancy.
Hence, if buoyancy is excluded, we should not separately include pressure force again.
- Other actual forces acting on the bubble
Now, excluding buoyancy, the remaining forces are:
- Gravity: the bubble contains gas, so it has mass and therefore weight.
- Viscous force: as the bubble rises through the liquid, the liquid opposes its motion by viscosity.
Thus, besides buoyancy, the bubble experiences:
- Check options
-
A: Only the force of gravity
Incorrect, because viscous drag also acts while the bubble moves upward. -
B: The force due to gravity and the force due to the pressure of the liquid
Incorrect, because the net pressure force is the buoyant force itself, already excluded. -
C: The force due to gravity, the force due to the pressure of the liquid and the force due to viscosity of the liquid
Incorrect, because pressure force is not separate from buoyancy. -
D: The force due to gravity and the force due to viscosity of the liquid
Correct.
- Final answer
The correct option is:
- Comparison with stored answer
Stored correct answer: D
Derived answer: D
So, the derived answer agrees with the stored answer.
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