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GATE 2020 AE – Question 28

Structures · Structural dynamics: free and forced vibration of SDOF systems and free vibration of 2-DOF systems · 1 mark · Multiple choice

A rectangular cantilever aluminium beam has first natural frequency ω rad/s. If length doubles with material and cross section unchanged, its first frequency becomes

  1. $\omega/4$
  2. $4\omega$
  3. $\omega/16$
  4. $16\omega$

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Correct answer: (A) $\omega/4$

Explanation

For an Euler–Bernoulli cantilever, $\omega_1=\beta_1^2\sqrt{EI/(\rho A)}/L^2$, with unchanged dimensionless mode constant β₁. Doubling L multiplies frequency by 1/4, so A.

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