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⚛️ Physics  ·  Oscillations  ·  NEET & JEE

A uniform rod of length 1.5 m is pivoted at one end and swings as a physical pendulum (I = mL<sup>2</sup>/3, centre of mass at L/2). Taking g = 10 m/s<sup>2</sup>, its time period is:

Answer: 1.99 s.

  • A 1.99 s
  • B 2.43 s
  • C 1.57 s
  • D 2.81 s

Correct answer: A. 1.99 s

Explanation: T = 2&pi;&radic;(I/mgd) = 2&pi;&radic;((mL<sup>2</sup>/3)/(mg&middot;L/2)) = 2&pi;&radic;(2L/3g) = 2&pi;&radic;(2&times;1.5/30) = 2&pi;&radic;0.1 = 1.99 s.

Displacement, Velocity, Acceleration in SHMx(t)v(t)a(t)v leads x by 90°; a is exactly out of phase with x (a = −ω²x)

In SHM, displacement and velocity are 90° out of phase (v is maximum when x=0, and zero when x is extreme), while acceleration is always exactly opposite in sign to displacement, consistent with a = −ω²x.

Concept context

Simple harmonic motion, spring-mass, pendulum, energy in SHM, and resonance.

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