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Forces on Submerged Bodies MCQs - Fluid Mechanics
Forces on Submerged Bodies MCQs - Fluid Mechanics: This section contains the multiple-choice questions and answers on the fluid mechanics chapter Dimensional and Model Analysis. practice these MCQs to learn and enhance the knowledge of Dimensional and Model Analysis.
List of Fluid Mechanics - Forces on Submerged Bodies MCQs
1. What is the force exerted by a flowing fluid on a stationary body called?
- Tensile force
- Drag force
- Buoyant force
- Gravitational force
Answer: B) Drag force
Explanation:
The drag force, which resists the motion of the body through the fluid, is the force a moving fluid applies on a stationary body.
2. Which of the following shapes typically experiences the least drag force when moving through a fluid?
- Sphere
- Cylinder
- Cube
- Irregular shape
Answer: A) Sphere
Explanation:
Among the given options, a sphere typically experiences the least drag force due to its streamlined shape, which minimizes resistance.
3. Which dimensionless group is commonly used to describe the drag force on an object moving through a fluid?
- Reynolds number (Re)
- Mach number (Ma)
- Strouhal number (St)
- Froude number (Fr)
Answer: A) Reynolds number (Re)
Explanation:
The Reynolds number is used to describe the drag force, particularly fluid flow and viscosity effects.
4. What is the primary factor contributing to pressure drag on a submerged body?
- Viscosity of the fluid
- Shape and form of the body
- Speed of the body through the fluid
- Buoyant force acting on the body
Answer: B) Shape and form of the body
Explanation:
Pressure drag, also known as form drag, is primarily influenced by the shape and form of the submerged body. Streamlined shapes reduce pressure drag.
5. How can friction drag be reduced on a submerged body?
- By reducing the viscosity of the fluid
- By increasing the speed of the body through the fluid
- By increasing the body's surface roughness
- By using smooth and streamlined body shapes
Answer: D) By using smooth and streamlined body shapes
Explanation:
Friction drag can be minimized by using smooth and streamlined body shapes that reduce skin friction with the fluid.
6. In which scenario is pressure drag more significant than friction drag?
- High-speed aircraft flying at altitude
- Submarines moving at low speeds
- Cars traveling on a rough road
- Bicycles moving on a smooth road
Answer: B) Submarines moving at low speeds
Explanation:
In scenarios where the body moves at low speeds, pressure drag (form drag) can be more significant than friction drag (viscous drag), especially if the body's shape is not streamlined.
7. Why are streamlined bodies used in fluid dynamics?
- To increase fluid resistance
- To make the body float easily
- To minimize pressure variations
- To maximize turbulence
Answer: C) To minimize pressure variations
Explanation:
Streamlined bodies are designed to minimize pressure variations and reduce drag in a fluid flow.
8. What is the primary advantage of using streamlined bodies in engineering applications?
- Increased fluid resistance
- Reduced energy efficiency
- Minimized drag and improved efficiency
- Irrelevant to engineering applications
Answer: C) Minimized drag and improved efficiency
Explanation:
Streamlined bodies reduce drag and improve the efficiency of fluid flow in engineering applications.
9. Which of the following is a characteristic feature of a bluff body?
- Low drag
- Smooth flow separation
- High pressure on its front surface
- Minimal wake region
Answer: C) High pressure on its front surface
Explanation:
A bluff body typically has high pressure on its front surface due to flow separation.
10. According to Stokes' Law, for very small spheres (low Reynolds number), the drag force is:
- Directly proportional to the sphere's radius
- Proportional to the sphere's volume
- Independent of the sphere's radius
- Inversely proportional to the sphere's radius
Answer: A) Directly proportional to the sphere's radius
Explanation:
Stokes' Law states that for small spheres at low Reynolds numbers, the drag force is directly proportional to the radius of the sphere.
11. What happens to an object's terminal velocity as its mass increases?
- Terminal velocity increases
- Terminal velocity decreases
- Terminal velocity remains the same
- Terminal velocity depends on the shape, not the mass
Answer: C) Terminal velocity remains the same.
Explanation:
The terminal velocity of an object is independent of its mass, assuming the shape and fluid properties remain constant.
12. Terminal velocity is influenced by which of the following factors?
- Fluid density and viscosity
- Object's mass and shape
- Gravitational acceleration
- All of the above
Answer: D) All of the above
Explanation:
Terminal velocity depends on the object's mass, shape, fluid density, viscosity, and gravitational acceleration.
13. How is lift typically generated on an airfoil?
- By reducing the airfoil's speed
- By increasing the airfoil's surface area
- By creating a pressure difference between the upper and lower surfaces
- By increasing the airfoil's weight
Answer: C) By creating a pressure difference between the upper and lower surfaces
Explanation:
A lift on an airfoil is generated by creating a pressure difference between the upper and lower surfaces, which results in an upward force
14. How does an increase in the angle of attack affect lift on an airfoil?
- Increases lift
- Decreases lift
- does not affect lift
- Increases drag but not lift
Answer: A) Increases lift
Explanation:
Increasing the angle of attack typically increases the lift generated by an airfoil up to a certain point, after which it may stall and lift decreases.
15. In the Magnus Effect, the direction of the force acting on a spinning object is:
- Parallel to the axis of rotation
- the same direction as the object is moving
- Perpendicular to the direction of motion
- Opposite to the direction of rotation
Answer: C) Perpendicular to the direction of motion.
Explanation:
The Magnus Effect creates a force that is perpendicular to the direction of motion of the spinning object.
16. What happens to the drag force on a cylinder when its diameter is increased while keeping other factors constant?
- The drag force increases proportionally
- The drag force decreases proportionally
- The drag force increases exponentially
- The drag force remains unchanged
Answer: A) The drag force increases proportionally.
Explanation:
Increasing the diameter of a cylinder while keeping other factors constant results in a proportional increase in drag force due to the increased surface area exposed to the fluid flow.