Math Problem Statement

Strings A and B have the same length and the same tension, but the mass of String B is 2.25 times the mass of string A. Both are vibrating at the same frequency. Which pair (if any) of the diagrams below correctly illustrates possible standing waves on strings A and B?

If none are possible, choose "none". Select one

A has one half wave, B is a full wave A is a full wave, B has 1 and a half waves A has half a wave, B has one and a half waves, A has a wave, B has half a wave None of the illustrations are correct.

Solution

To determine which configuration could correctly illustrate standing waves on strings A and B, let's analyze the relationship between the properties of the two strings and their waveforms.

Given information:

  1. Length and Tension: Both strings have the same length and the same tension.
  2. Mass: String B has 2.25 times the mass of String A.
  3. Frequency: Both strings vibrate at the same frequency.

Understanding the Wave Speed Relationship:

The wave speed vv on a string is given by the formula: v=Tμv = \sqrt{\frac{T}{\mu}} where:

  • TT is the tension in the string (same for both strings),
  • μ\mu is the linear mass density of the string (mass per unit length).

Since String B has 2.25 times the mass of String A, it has 2.25 times the linear mass density as well. Let μA\mu_A be the mass density of String A, and μB=2.25μA\mu_B = 2.25 \mu_A for String B.

Substituting into the wave speed formula, we find that: vB=TμB=T2.25μA=vA2.25=vA1.5v_B = \sqrt{\frac{T}{\mu_B}} = \sqrt{\frac{T}{2.25 \mu_A}} = \frac{v_A}{\sqrt{2.25}} = \frac{v_A}{1.5} This shows that the wave speed on String B is slower than on String A by a factor of 1.5.

Relating Wave Speed to Wavelength:

Since both strings vibrate at the same frequency ff, and wave speed vv is related to frequency and wavelength λ\lambda by v=fλv = f \lambda, we find: λB=vBf=vA1.5f=λA1.5\lambda_B = \frac{v_B}{f} = \frac{v_A}{1.5 f} = \frac{\lambda_A}{1.5} This implies that the wavelength on String B is shorter than that on String A by a factor of 1.5.

Evaluating the Options:

  1. Option 1: A has one half wave, B has a full wave

    • Here, the wavelength on String B would be half that of String A, implying λB=λA2\lambda_B = \frac{\lambda_A}{2}.
    • This is inconsistent with our calculation (λB=λA1.5\lambda_B = \frac{\lambda_A}{1.5}).
  2. Option 2: A is a full wave, B has 1 and a half waves

    • Here, the wavelength on String B is two-thirds that of String A (λB=λA1.5\lambda_B = \frac{\lambda_A}{1.5}), which matches our calculation.
    • This option is possible.
  3. Option 3: A has half a wave, B has one and a half waves

    • Here, the wavelength on String B would be one-third that of String A, implying λB=λA3\lambda_B = \frac{\lambda_A}{3}.
    • This does not match our calculation.
  4. Option 4: A has a wave, B has half a wave

    • This would imply that the wavelength on String B is double that of String A, which does not match our calculation.
  5. Option 5: None of the illustrations are correct

    • Since Option 2 is valid, this choice is incorrect.

Conclusion:

The correct answer is: Option 2: A is a full wave, B has 1 and a half waves

Would you like more details or have any questions?


Related Questions:

  1. How does changing the frequency affect the wavelengths on strings A and B?
  2. What happens to the wave speed if the tension in both strings is doubled?
  3. If the mass of String B were increased to 4 times that of String A, how would the wavelength on B compare to that on A?
  4. Why does increasing the mass of a string reduce the wave speed?
  5. How would the standing wave patterns change if String A had a higher frequency than String B?

Tip: Remember that wave speed in a string depends on both its tension and its linear mass density, making heavier strings vibrate with shorter wavelengths at the same frequency.

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Math Problem Analysis

Mathematical Concepts

Wave Mechanics
Standing Waves
Wave Speed
Wavelength

Formulas

Wave speed formula: v = √(T/μ)
Relationship between wave speed and frequency: v = fλ

Theorems

Wave speed is inversely proportional to the square root of linear mass density for a given tension.

Suitable Grade Level

Grades 10-12