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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Simple Harmonic Motion

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Simple Harmonic Motion

Suspended from a nail in a wall, a closed circular wire experiences...

Suspended from a nail in a wall, a closed circular wire experiences small oscillations with an amplitude of 2^{}^{{}^{\circ}} and a time period of 2 s2 \text{ s}. Compute the acceleration of the particle on the wire farthest from the point of suspension when it is at an extreme position. Take g=π2 m/s2g = \pi^2 \text{ m/s}^2.

Options

  1. A17 cm/s217 \text{ cm/s}^2 towards the mean position
  2. B34 cm/s234 \text{ cm/s}^2 away from the mean position
  3. C68 cm/s268 \text{ cm/s}^2 towards the mean position
  4. D34 cm/s234 \text{ cm/s}^2 towards the mean position

Correct answer

D. 34 cm/s234 \text{ cm/s}^2 towards the mean position

Step-by-step solution

For a closed circular wire (ring) of radius RR suspended from a point on its circumference and oscillating in its own plane, the moment of inertia about the point of suspension is I=mR2+mR2=2mR2I = mR^2 + mR^2 = 2mR^2.

The distance from the point of suspension to the center of mass is d=Rd = R.

The time period of this physical pendulum is given by:

T=2πImgd=2π2mR2mgR=2π2RgT = 2\pi \sqrt{\dfrac{I}{mgd}} = 2\pi \sqrt{\dfrac{2mR^2}{mgR}} = 2\pi \sqrt{\dfrac{2R}{g}}

Given T=2 sT = 2 \text{ s} and g=π2 m/s2g = \pi^2 \text{ m/s}^2, substituting these values yields:

2=2π2Rπ22 = 2\pi \sqrt{\dfrac{2R}{\pi^2}}

1=2R⇒2R=1 m1 = \sqrt{2R} \Rightarrow 2R = 1 \text{ m}

The farthest point on the wire from the point of suspension is at a distance L=2R=1 mL = 2R = 1 \text{ m}.

The angular frequency of oscillation is ω=2πT=π rad/s\omega = \dfrac{2\pi}{T} = \pi \text{ rad/s}.

The angular amplitude is \theta_0 = 2^{}^{{}^{\circ}} = 2 \times \dfrac{\pi}{180} = \dfrac{\pi}{90} \text{ rad}.

At the extreme position, the angular velocity is zero, so the radial (centripetal) acceleration is zero. The acceleration is purely tangential.

The maximum angular acceleration at the extreme position is α=ω2θ0\alpha = \omega^2 \theta_0.

The linear acceleration of the farthest point is:

a=Lα=Lω2θ0a = L \alpha = L \omega^2 \theta_0

Substituting the values:

a=1×π2×π90=π390 m/s2a = 1 \times \pi^2 \times \dfrac{\pi}{90} = \dfrac{\pi^3}{90} \text{ m/s}^2

Converting to cm/s2\text{cm/s}^2:

a=100π390 cm/s2=10π39 cm/s2a = \dfrac{100 \pi^3}{90} \text{ cm/s}^2 = \dfrac{10 \pi^3}{9} \text{ cm/s}^2

Using π≈3.14\pi \approx 3.14, π3≈31.0\pi^3 \approx 31.0:

a≈10×31.09≈34.4 cm/s2≈34 cm/s2a \approx \dfrac{10 \times 31.0}{9} \approx 34.4 \text{ cm/s}^2 \approx 34 \text{ cm/s}^2

In simple harmonic motion, the acceleration is always directed towards the mean position.

Answer: 34 cm/s234 \text{ cm/s}^2 towards the mean position
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