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) is true because the definition of dynamic equilibrium is the state where a body moves with uniform velocity (no acceleration).
2. Reason (R) is true because a cyclist or sprinter maintaining a steady state of motion is successfully balancing the driving forces against resistive forces (like air resistance and friction).
3. Since the examples in R perfectly illustrate the definition provided in A, R is the correct explanation for A.
Step 3: Final Answer:
Both statements are true, and R explains A.

Answer 2

This is an Assertion-Reason question about dynamic equilibrium in biomechanics. To answer it, we need to independently verify Assertion (A) and Reason (R), then check whether R logically explains A, and match that conclusion against the four given option statements.

1. Option 1 (Both A and R true, R is the correct explanation of A): Dynamic equilibrium means the net force on a moving body is zero, so it continues at constant velocity, exactly as stated in A. A cyclist pedalling at a steady speed and a sprinter holding a fixed running posture are both bodies experiencing zero net force while in motion, which is exactly what dynamic equilibrium describes. Since R's examples are direct instances of the state defined in A, R does explain A, so this option holds.
2. Option 2 (Both true, R does not explain A): This would require R to be a true but unrelated statement. Here, however, R is not unrelated; it names concrete cases of the very phenomenon A defines. Since the link between R and A is direct, this option is ruled out.
3. Option 3 (A true, R false): For this option to hold, the cyclist and sprinter examples would have to be wrong illustrations of dynamic equilibrium. But a cyclist moving at constant speed and a sprinter maintaining a steady running form are textbook cases of balanced forces in motion, so R cannot be labelled false. This option fails.
4. Option 4 (A false, R true): This would require the definition of dynamic equilibrium in A to be incorrect. Constant velocity with no change in speed or direction is precisely the standard definition of dynamic equilibrium, so A cannot be false. This option is also ruled out.

Only the first option survives this check: both statements are individually correct, and the examples in R are genuine applications of the definition given 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).