Priti Patel
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A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.

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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-13

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  1. 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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  2. 1. Definition of Work in Physics:
    – Work is defined as the product of force and displacement in the direction of the force applied.

    2. Force Exerted by the Person:
    – The person exerts a force against gravity to hold the bundle of hay over his head, countering the weight of the hay.

    3. Absence of Displacement:
    – Despite exerting a force to hold the bundle, there is no vertical displacement or change in the position of the hay during the 30 minutes.
    – The bundle of hay remains stationary and does not move vertically while being held.

    4. Work Calculation Criteria:
    – For work to be done, there must be a displacement in the direction of the force applied.
    – Work is calculated as W = F x d x cos(θ), where F is force, (d) is displacement, and (θ) is the angle between force and displacement.

    5. No Displacement, No Work Done:
    – In this scenario, although the person exerts a force to counteract gravity, there is no vertical movement or displacement of the hay.
    – The absence of vertical displacement means that the force applied by the person does not result in any work being done on the bundle of hay.

    6. Explanation of Fatigue:
    – The person may feel tired due to muscular effort expended to maintain the position of the hay against gravity for an extended period.
    – However, the fatigue is not due to the performance of physical work in the physics sense as there is no displacement in the direction of the force applied.

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