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MHT CET 2021 (23 Sep, Shift 2) · Speed of Waves

Speed of Waves question from MHT CET 2021 (23 Sep, Shift 2)

Q26MHT CET 2021 · 23 SEP · SHIFT 2Difficult

Speed of Waves

A uniform rope of length 12 m12\text{ m} and mass 6 kg6\text{ kg} hangs vertically from the rigid support. A block of mass 2 kg2\text{ kg} is attached to the free end of the rope. A transverse pulse of wavelength 0.06 m0.06\text{ m} is produced at the lower end of the rope. The wavelength of the pulse when it reaches the top of the rope is

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Answer: (c)

  1. Frequency stays the same along the rope, so λ∝v∝T\lambda \propto v \propto \sqrt{T}.
  2. Tension at the bottom: T1=2gT_1 = 2g; at the top: T2=(6+2)g=8gT_2 = (6+2)g = 8g.
  3. λ2λ1=8g2g=2⇒λ2=2×0.06=0.12 m\dfrac{\lambda_2}{\lambda_1} = \sqrt{\dfrac{8g}{2g}} = 2 \Rightarrow \lambda_2 = 2 \times 0.06 = 0.12\text{ m}
  4. So the answer is (c) 0.12 m0.12\text{ m}.
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