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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.

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