JEE Mains · Physics · STD 11 - 13. oscillations

Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Knowing initial position \(x_0\) and initial momentum \(p_0\) is enough to determine the position and momentum at any time \(t\) for a simple harmonic motion with a given angular frequency \(\omega\).
Reason (R): The amplitude and phase can be expressed in terms of \(x_0\) and \(\mathrm{p}_0\).
In the light of the above statements, choose the correct answer from the options given below :

A (A) is false but (R) is true
B (A) is true but (R) is false
C Both (A) and (R) are true but (R) is NOT the correct explanation of (A)
D Both \((\mathbf{A})\) and \((\mathbf{R})\) are true and \((\mathbf{R})\) is the correct explanation of \((\mathbf{A})\)

Verified Solution

Answer & Solution

Correct Answer

(D) Both \((\mathbf{A})\) and \((\mathbf{R})\) are true and \((\mathbf{R})\) is the correct explanation of \((\mathbf{A})\)

Step-by-step Solution

Detailed explanation

\(\begin{aligned} & \text { If we express position } x(t)=A \sin (\omega t+\phi) \\ & \text { then } x_0=A \sin \phi \\ & v_0=A \omega \cos \phi \\ & \Rightarrow \tan \phi=\frac{\omega x_0}{v_0} \\ & A=\sqrt{x_0^2+\frac{v_0^2}{\omega^2}}\end{aligned}\) Hence both position and…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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