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JEE Main 201510 AprilOnline
Exam
JEE Main
Year
2015
Date
10 April
Mode
Online
Subject
Physics
Chapter
Oscillations

JEE Main 2015 · 10 April · Online · Physics · Oscillations

A simple harmonic oscillator of angular frequency 2rad s ^ - 1 is...

A simple harmonic oscillator of angular frequency 2rads−12rad{s}^{- 1} is acted upon by an external force F=sintN.F = sin tN .If the oscillator is at rest in its equilibrium position at t=0,t = 0, its position at later times is proportional to:

Options

  1. Asint+12cos⁡2tsin t + \dfrac{1}{2}\cos 2t
  2. Bcos⁡t−12sin⁡2t\cos t - \dfrac{1}{2}\sin 2t
  3. Csint−12sin⁡2tsin t - \dfrac{1}{2}\sin 2t
  4. Dsint+12sin⁡2tsin t + \dfrac{1}{2}\sin 2t

Correct answer

C. sint−12sin⁡2tsin t - \dfrac{1}{2}\sin 2t

Step-by-step solution

It is given that oscillator at rest at t=0t = 0 i.e. at t=0t = 0, v=0v = 0. So, in option, we can check by putting v=dxdt=0v = \dfrac{dx}{dt} = 0.

(1) Ifx∝sint+12cos⁡2tIfx ∝ sin t + \dfrac{1}{2}\cos 2t

⟹v∝cost+12×2(−sin⁡2t)⟹ v ∝ cos t + \dfrac{1}{2} \times 2 ( - \sin 2t )

⟹att=0,v∝1−0≠0⟹ att = 0, v ∝ 1 - 0 \ne 0

(2) Ifx∝cost−12sintIfx ∝ cos t - \dfrac{1}{2}sin t

⟹v∝−sint−12cost⟹ v ∝ - sin t - \dfrac{1}{2}cos t

⟹att=0,v∝−12≠0⟹ att = 0, v ∝ - \dfrac{1}{2} \ne 0

(3) Ifx∝sint−12sin⁡2tIfx ∝ sin t - \dfrac{1}{2}\sin 2t

thenυ∝cost−12×2cos⁡2tthenυ ∝ cos t - \dfrac{1}{2} \times 2\cos 2t

⟹att=0,v∝1−1=0⟹ att = 0, v ∝ 1 - 1 = 0

(4) Ifx∝sint+12sin⁡2tIfx ∝ sin t + \dfrac{1}{2}\sin 2t

⟹v∝cost+12×2cos⁡2t⟹ v ∝ cos t + \dfrac{1}{2} \times 2\cos 2t

⟹att=0,v∝1+1⟹ att = 0, v ∝ 1 + 1

⟹v∝2≠0⟹ v ∝ 2 \ne 0

∴inoption(3)v=0att=0∴ inoption\left(3\right)v = 0att = 0
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