MCQEasyJEE 2023Simple Harmonic Motion (SHM)

JEE Physics 2023 Question with Solution

For a simple harmonic motion in a mass spring system shown, the surface is frictionless. When the mass of the block is 1kg1 \, \text{kg}, the angular frequency is ω1\omega_1. When the mass block is 2kg2 \, \text{kg} the angular frequency is ω2\omega_2. The ratio ω2ω1\frac{\omega_2}{\omega_1} is:

A horizontal spring attached to a wall on the left and connected to a block on a frictionless horizontal surface.
  • A

    2\sqrt{2}

  • B

    12\frac{1}{\sqrt{2}}

  • C

    22

  • D

    12\frac{1}{2}

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: A mass-spring system on a frictionless surface. For mass m1=1kgm_1 = 1 \, \text{kg}, angular frequency is ω1\omega_1. For mass m2=2kgm_2 = 2 \, \text{kg}, angular frequency is ω2\omega_2.

Find: The ratio ω2ω1\frac{\omega_2}{\omega_1}.

For a spring-mass system,

ω=km\omega = \sqrt{\frac{k}{m}}

Therefore,

ω1=km1,ω2=km2\omega_1 = \sqrt{\frac{k}{m_1}}, \qquad \omega_2 = \sqrt{\frac{k}{m_2}}

Taking the ratio,

ω2ω1=m1m2\frac{\omega_2}{\omega_1} = \sqrt{\frac{m_1}{m_2}}

Substituting m1=1m_1 = 1 and m2=2m_2 = 2,

ω2ω1=12=12\frac{\omega_2}{\omega_1} = \sqrt{\frac{1}{2}} = \frac{1}{\sqrt{2}}

Therefore, the correct option is B. The solution labels it as option D, but the listed value matches option B.

Common mistakes

  • Using ωm\omega \propto \sqrt{m} instead of ω1m\omega \propto \frac{1}{\sqrt{m}}. This reverses the dependence on mass. For a spring-mass system, increasing mass decreases angular frequency.

  • Taking the ratio as ω2ω1=m2m1\frac{\omega_2}{\omega_1} = \sqrt{\frac{m_2}{m_1}}. The mass terms appear inverted because ω=km\omega = \sqrt{\frac{k}{m}}, so the correct ratio is m1m2\sqrt{\frac{m_1}{m_2}}.

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