ANS:B - the component being parallel to theflow direction.

The definition of drag in fluid dynamics is: Drag is the force component exerted on an immersed object parallel to the flow direction. Here’s an explanation:

• Parallel to the flow direction: Drag force is the resistance force exerted by a fluid on an object moving through it in the direction opposite to its motion. This force acts parallel to the relative motion between the fluid and the object.

• Passing the centroid of the body at 60° to the direction of motion: This describes a specific case of a force component acting at an angle to the direction of motion, not the definition of drag itself.
• The component being parallel to the flow direction: This is the correct definition of drag force, as explained above.
• The component being normal to the flow direction: This describes a perpendicular force component to the flow direction, which is not characteristic of drag force.
• None of these: While some of the options describe aspects related to forces acting on objects in fluids, the correct definition of drag is specifically the force component parallel to the flow direction.