Simple Harmonic Motion 5 Question 3

3. A simple pendulum of length 1m is oscillating with an angular frequency 10rad/s. The support of the pendulum starts oscillating up and down with a small angular frequency of 1rad/s and an amplitude of 102m. The relative change in the angular frequency of the pendulum is best given by

(a) 1rad/s

(b) 105rad/s

(c) 103rad/s

(d) 101rad/s

(2019 Main, 11 Jan II)

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Answer:

Correct Answer: 3. (c)

Solution:

  1. We know that time period of a pendulum is given by

T=2πlg

So, angular frequency ω=2πT=gl

Now, differentiate both side w.r.t g

dωdg=12gldω=dg2gl

By dividing Eq. (ii) by Eq. (i), we get

dωω=dg2g

Or we can write

Δωω=Δg2g

As Δg is due to oscillation of support.

Δg=2ω2A

(ω11rad/s, support)

Putting value of Δg in Eq. (iii) we get

Δωω=122ω12Ag=ω12Ag;(A=102m2)Δωω=1×10210=103rad/s



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