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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}. Evaluate the acceleration of the particle on the wire farthest from the point of suspension as it passes through its mean position. Take g=π2 m/s2g = \pi^2 \text{ m/s}^2.

Options

  1. A3.6 cm/s23.6 \text{ cm/s}^2 away from the point of suspension
  2. B1.2 cm/s21.2 \text{ cm/s}^2 towards the point of suspension
  3. C1.2 cm/s21.2 \text{ cm/s}^2 away from the point of suspension
  4. D2.4 cm/s22.4 \text{ cm/s}^2 towards the point of suspension

Correct answer

B. 1.2 cm/s21.2 \text{ cm/s}^2 towards the point of suspension

Step-by-step solution

The moment of inertia of the closed circular wire (ring) about the point of suspension on its circumference is I=Icm+MR2=2MR2I = I_{cm} + M R^2 = 2 M R^2.

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

The time period of the physical pendulum is given by:

T=2πIMgd=2π2MR2MgR=2π2RgT = 2 \pi \sqrt{\dfrac{I}{M g d}} = 2 \pi \sqrt{\dfrac{2 M R^2}{M g R}} = 2 \pi \sqrt{\dfrac{2 R}{g}}

Given T=2 sT = 2 \text{ s} and g=π2 m/s2g = \pi^2 \text{ m/s}^2, we have:

2=2π2Rπ2⇒1=2R⇒2R=1 m2 = 2 \pi \sqrt{\dfrac{2 R}{\pi^2}} \Rightarrow 1 = \sqrt{2 R} \Rightarrow 2 R = 1 \text{ m}

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

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

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

The maximum angular velocity of the pendulum as it passes through the mean position is Ω=θ0ω=π290 rad/s\Omega = \theta_0 \omega = \dfrac{\pi^2}{90} \text{ rad/s}.

At the mean position, the angular acceleration is zero, so the tangential acceleration is zero. The acceleration of the farthest point is purely centripetal:

a=Ω2L=(π290)2×1=π48100 m/s2a = \Omega^2 L = \left( \dfrac{\pi^2}{90} \right)^2 \times 1 = \dfrac{\pi^4}{8100} \text{ m/s}^2

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

a=π481 cm/s2a = \dfrac{\pi^4}{81} \text{ cm/s}^2

Using π2≈9.87\pi^2 \approx 9.87, we get π4≈97.4\pi^4 \approx 97.4.

a≈97.481≈1.2 cm/s2a \approx \dfrac{97.4}{81} \approx 1.2 \text{ cm/s}^2

The direction of this centripetal acceleration is towards the center of its circular path, which is the point of suspension.

Answer: 1.2 cm/s21.2 \text{ cm/s}^2 towards the point of suspension
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