Question

Assertion (A): When an object or body is moving at a constant velocity, with no changes in speed or direction, it is dynamic equilibrium.
Reason (R): A cyclist in motion or the body position maintained by a sprinter on the track while running are examples of dynamic equilibrium.

• A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Remember: Equilibrium = Net Force is Zero. If the body is still, it's Static. If the body is moving at a steady speed in a straight line, it's Dynamic.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:  
Equilibrium in biomechanics is divided into two types: Static (at rest) and Dynamic (in motion). Dynamic equilibrium occurs when all forces acting on a moving body are balanced, resulting in constant velocity. 

Step 2: Detailed Explanation: 
 

1. Assertion (A): The definition of dynamic equilibrium is the state where a body moves with uniform velocity (no acceleration). 
    
2. Reason (R): A cyclist or sprinter maintaining a steady state of motion is successfully balancing the driving forces against resistive forces (such as air resistance and friction). 
    
3. Conclusion: Since the examples in Reason (R) perfectly illustrate the definition provided in Assertion (A), Reason (R) is the correct explanation for Assertion (A). 
    

Step 3: Final Answer: 
Both statements are true, and Reason (R) explains Assertion (A).

Answer 2

Dynamic equilibrium is best understood through Newton's First Law: a body continues in its state of motion, constant speed, fixed direction, unless acted on by an unbalanced force. Applying this idea to the statement and its reason shows how they connect.

1. Assertion (A): A body moving with constant velocity, with no change in speed or direction, has zero acceleration. By Newton's First Law, this only happens when all forces acting on the body cancel out. This balanced-force, constant-velocity state is what dynamic equilibrium means, so A is a correct statement.
2. Reason (R): A cyclist cruising at a fixed pace pushes against air resistance and rolling friction with just enough pedalling force to cancel them out, so the net force is zero and the velocity stays constant. A sprinter holding a consistent running posture through a stride cycle is similarly balancing propulsive and resistive forces from one stride to the next. Both are real, verifiable examples of bodies in motion with balanced forces, so R is also correct.
3. Linking A and R: Since R's examples describe exactly the balanced-force, constant-velocity condition that A defines as dynamic equilibrium, R does not merely happen to be true alongside A, it demonstrates A. That makes R the correct explanation of A, not just an unrelated true statement.

So both parts of the statement are accurate, and the reasoning in R is what justifies the assertion in A.

Therefore, the correct answer is Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of the Assertion (A).