Drag is defined as the force exerted by a flowing fluid on a slid body
- Ain the direction of flowCorrect
- Bperpendicular to the direction of flow
- Cin the direction which is at an angle of 45º to the direction of flow
- Din the opposite direction of flow
Solution
Concept
Definition and direction of drag force
Formula
NONE
Step-by-step solution
1. When a fluid flows past a body, it exerts a total dynamic force on the surface of the body. 2. The component of this force acting parallel to the direction of relative fluid flow is defined as drag. 3. Therefore, drag force is exerted on a solid body in the direction of flow. Answer: A
Explanation
Drag force is the resistive force exerted by a fluid on an immersed object parallel to the relative motion between the fluid and the body. Because it acts parallel to the motion, drag always acts in the direction of fluid flow. In contrast, lift force acts perpendicular to the flow direction.
Why the other options are wrong
B) The force exerted by a flowing fluid perpendicular to the direction of flow is defined as lift force. C) Drag acts parallel to the flow direction, not at an angle of 45º. D) Drag acts in the direction of fluid flow relative to the body, not in the opposite direction.
Shortcut
Drag force acts in the direction of flow, while Lift acts perpendicular to flow.
Common mistake
Confusing drag force (parallel to flow) with lift force (perpendicular to flow).
Correct answer: A) in the direction of flow