HC Verma Chapter 15 Problem 53 — standing wave identification from superposition

Problem Statement

Solve the oscillation/wave problem: Solve the oscillation/wave problem: $y=2\sin(3x-6t)+2\sin(3x+6t)$. Standing or traveling? Find nodes. Opposite-direction waves of same amplitude/frequency superpose into standing wave Step 1: Using sum-to-product: $y=4\sin(3x)\cos(6t)$ — standing wave. Step 2: Nodes: $3x=n\pi$, $x=n\pi/3$ m. $$\boxe

Given Information

  • See problem statement for all given quantities.

Physical Concepts & Formulas

This problem applies fundamental physics principles to the scenario described. The solution requires identifying the relevant conservation laws and equations of motion, then solving systematically with careful attention to units and sign conventions.

  • See the step-by-step solution for the specific equations applied.
  • All quantities are in SI units unless otherwise stated.

Step-by-Step Solution

Step 1 — Verify the result: Check units, limiting cases, and order of magnitude to confirm the answer is physically reasonable.

Step 2 — Verify the result: Check units, limiting cases, and order of magnitude to confirm the answer is physically reasonable.

Step 3 — Verify the result: Check units, limiting cases, and order of magnitude to confirm the answer is physically reasonable.

Worked Calculation

$$\boxe

Given Information

  • Mass $m$ and spring constant $k$ (or equivalent), or wave parameters
  • Initial conditions (amplitude $A$, phase $\phi$) as given

Physical Concepts & Formulas

Simple harmonic motion arises whenever a restoring force is proportional to displacement: $F = -kx$. Newton’s second law then gives $\ddot{x} = -(k/m)x = -\omega_0^2 x$, whose solution is $x(t) = A\cos(\omega_0 t + \phi)$. The total mechanical energy $E = \frac{1}{2}kA^2$ is constant for ideal SHM. In waves, the same equation appears but in space-time: $\partial^2 y/\partial t^2 = v^2\,\partial^2 y/\partial x^2$.

  • $\omega_0 = \sqrt{k/m}$ — angular frequency
  • $T = 2\pi/\omega_0 = 2\pi\sqrt{m/k}$ — period
  • $x(t) = A\cos(\omega_0 t + \phi)$ — general SHM solution
  • $E = \tfrac{1}{2}kA^2$ — total mechanical energy
  • $v = f\lambda$ — wave speed

Step-by-Step Solution

Step 1 — Identify the restoring force and write the equation of motion.

Step 2 — Find $\omega_0$: $\omega_0 = \sqrt{k/m}$

Step 3 — Apply initial conditions to find $A$ and $\phi$.

Step 4 — Compute quantities asked (period, frequency, max velocity $v_{max}=A\omega_0$, max acceleration $a_{max}=A\omega_0^2$).

Worked Calculation

Substituting all values with units:

$$

$$

Answer

$$

Answer

$$\boxed{T = 2\pi\sqrt{m/k}}$$

Physical Interpretation

The numerical answer is physically reasonable — matching expected orders of magnitude and dimensional analysis. The result confirms the theoretical prediction and provides quantitative insight into the system’s behaviour.


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