Priti Patel
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Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?

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NCERT Solutions for Class 9 Science Chapter 11
Important NCERT Questions
Work and Energy
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Exercises Questions
Page No-159
Questions No-15

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2 Answers

  1. 1. Initial Energy States:
    – Potential Energy: When the pendulum bob is drawn to one side, it gains potential energy due to its height above the equilibrium position.
    – Kinetic Energy: Initially, the pendulum bob is at rest, so it possesses zero kinetic energy.

    2. Conversion of Potential to Kinetic Energy:
    – As the pendulum swings downward, potential energy converts into kinetic energy. At the lowest point of the swing, all potential energy is converted to kinetic energy.
    – The pendulum reaches its maximum kinetic energy at the bottom of the swing, moving at its maximum speed.

    3. Oscillation and Energy Transformation:
    – The pendulum continues to oscillate, with energy continuously transforming between potential and kinetic forms as it swings back and forth.

    4. Energy Dissipation:
    – Factors like air resistance, friction at the pivot, and internal friction cause the pendulum to lose energy gradually.
    – The lost energy transforms into less usable forms such as heat and sound, dissipating into the surroundings.

    5. Decrease in Amplitude:
    – As energy dissipates, the pendulum’s amplitude (maximum swing angle) decreases gradually with each swing.
    – Eventually, due to energy losses, the pendulum comes to rest at its equilibrium position.

    6. Conservation of Total Energy:
    – While the pendulum eventually stops moving, the total energy of the system (including the pendulum and its surroundings) remains constant.
    – Energy is not lost but rather transformed into less available forms, conforming to the law of conservation of energy.

    7. Energy Transformation Summary:
    – Initial potential energy is converted to kinetic energy during the swing.
    – Energy dissipates due to various factors, leading to a decrease in motion until the pendulum eventually comes to rest.
    – The total energy within the system and surroundings remains conserved, even though it becomes less available for useful work due to dissipation.

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  2. Get Hindi Medium and English Medium NCERT Solution for Class 9 Science to download.
    Please follow the link to visit website for first and second term exams solutions.
    https://www.tiwariacademy.com/ncert-solutions/class-9/science/chapter-11/

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