BAS 021 Physics I: Energy of a System
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What happens when the work done on a system is positive?

  • Energy is stored in the system.
  • Energy is conserved in the system.
  • Energy is transferred from the system.
  • Energy is transferred to the system. (correct)

    • When a weightlifter lowers weights, the work done by the weights on his hands is ___ while the work done by his hands on the weights is ___.

  • zero; positive
  • positive; zero
  • negative; positive
  • positive; negative (correct)

    • In the context of work done by a varying force, what is the requirement for a particle's displacement?

  • It can be negative only.
  • It can be small and variable. (correct)
  • It must be constant.
  • It must be along the y-axis.

    • What determines the work done by a constant force on an object?

    <p>The angle between the force and the displacement.</p> Signup and view all the answers

    What is true regarding the forces acting during the weightlifter's action of lowering weights?

    <p>Forces are equal and opposite according to Newton's third law.</p> Signup and view all the answers

    What characterizes work done by a conservative force?

    <p>It is independent of the path taken between two points.</p> Signup and view all the answers

    What is true about the work done by a conservative force over a closed path?

    <p>It is zero.</p> Signup and view all the answers

    Which of the following is NOT a conservative force?

    <p>Frictional force</p> Signup and view all the answers

    If a particle moves from point O to point C with different paths, what will be the work done by gravitational force?

    <p>It will be identical regardless of the path taken.</p> Signup and view all the answers

    What happens to the mechanical energy when a nonconservative force, like friction, is present?

    <p>It becomes lost as internal energy.</p> Signup and view all the answers

    What happens to the final kinetic energy of a system if the net work done on it is positive?

    <p>It is greater than the initial kinetic energy</p> Signup and view all the answers

    Which of the following equations represents the work done by the external force?

    <p>$W_{ext} = \frac{1}{2} m v_f^2 - \frac{1}{2} m v_i^2$</p> Signup and view all the answers

    What is the relationship between work, energy, and power in physics?

    <p>Energy is the ability to perform work, while power measures the speed of doing work.</p> Signup and view all the answers

    What is true about the acceleration of the electron as it travels through the plates?

    <p>It is constant and directed forward</p> Signup and view all the answers

    In the context of work done by a constant force, which factor does NOT influence the work performed?

    <p>The mass of the object being moved.</p> Signup and view all the answers

    If the final speed of the electron is less than the initial speed, what can be concluded about the work done?

    <p>The work done is negative</p> Signup and view all the answers

    Given that the speed of light is $3 \times 10^8 \text{ m/s}$, what is the final speed of the electron when it reaches 9.6% of the speed of light?

    <p>$2.88 \times 10^7 \text{ m/s}$</p> Signup and view all the answers

    What is the formula used to calculate work done by a constant force?

    <p>W ≡ F ∆r cos θ</p> Signup and view all the answers

    Which of the following best describes the role of conservative forces?

    <p>They do not depend on the path taken for work done.</p> Signup and view all the answers

    In the context of the work-kinetic energy theorem, what does $,W_{ext} = \Delta K$ signify?

    <p>The work done is equal to the change in kinetic energy</p> Signup and view all the answers

    How does the distance between the plates affect the force acting on an electron?

    <p>Increasing the distance decreases the force</p> Signup and view all the answers

    What unit is used to measure work in the International System of Units (SI)?

    <p>Joule</p> Signup and view all the answers

    Why does a weightlifter do no work on the weights while holding them still?

    <p>There is no displacement of the weights.</p> Signup and view all the answers

    Which of the following statements accurately describes the role of the electric force in the acceleration of the electron?

    <p>It is responsible for the acceleration of the electron</p> Signup and view all the answers

    Which statement about energy is true?

    <p>Energy can neither be created nor destroyed.</p> Signup and view all the answers

    What role does the angle θ play in the calculation of work done by a force?

    <p>It determines whether work is positive, negative, or zero.</p> Signup and view all the answers

    What is the final kinetic energy of the system given initial kinetic energy was zero and final velocity is $2.88 \times 10^{7}$ m/s?

    <p>$3.78 \times 10^{-16}$ J</p> Signup and view all the answers

    What is the work done on the system when lifting the book against gravity?

    <p>$3.78 \times 10^{-16}$ J</p> Signup and view all the answers

    What is the expression for gravitational potential energy?

    <p>$U_g = mgh$</p> Signup and view all the answers

    Given a mass $m = 9.11 \times 10^{-31}$ kg and a net force $F = 1.35 \times 10^{-14}$ N, what is the acceleration of the mass?

    <p>$1.48 \times 10^{16}$ m/s²</p> Signup and view all the answers

    If a book is lifted slowly with constant velocity, how does the kinetic energy of the system change?

    <p>Remains the same since there is no change in kinetic energy</p> Signup and view all the answers

    What is the relationship between work done and gravitational potential energy in this context?

    <p>Work done equals the change in gravitational potential energy.</p> Signup and view all the answers

    What value represents the net force exerted on the mass in this scenario?

    <p>$1.35 \times 10^{-14}$ N</p> Signup and view all the answers

    In the equation $t = \frac{v_{x,f} - v_{x,i}}{a_x}$, what does $t$ represent?

    <p>The time interval during the motion</p> Signup and view all the answers

    What happens to the gravitational potential energy when an object falls?

    <p>It increases because the height decreases.</p> Signup and view all the answers

    What factors determine the gravitational potential energy of an object?

    <p>Mass of the object and its vertical height above the ground.</p> Signup and view all the answers

    When lifting an object, what is true regarding work done?

    <p>The same amount of work is done regardless of the lifting method.</p> Signup and view all the answers

    What is the mechanical energy of a system comprised of kinetic and potential energies?

    <p>It is constant only in a conservative force field.</p> Signup and view all the answers

    What is an example of a nonconservative force?

    <p>Frictional force slowing down a sliding object.</p> Signup and view all the answers

    In the context of potential energy, what does a negative work indicate?

    <p>The object is losing gravitational potential energy.</p> Signup and view all the answers

    If a 2 kg book is dropped from a height of 1.4 m, what can be inferred about its change in potential energy as it falls to 0.05 m?

    <p>The potential energy change is negative.</p> Signup and view all the answers

    What are the two key properties of conservative forces?

    <p>Do not depend on path and always work in a closed loop.</p> Signup and view all the answers

    Study Notes

    BAS 021 Physics I: Energy of a System

    • The course covers fundamental physics concepts of work, energy, and power
    • Work is done when a force causes displacement of an object
    • Energy is the capacity to do work
    • Power is the rate of doing work (work per unit of time)

    Contents

    • Introduction to work, energy, and power
    • Work done by a constant force
    • Work done by a varying force
    • Kinetic energy and the work-kinetic energy theorem
    • Potential energy of a system
    • Conservative and nonconservative forces

    Introduction

    • Work, energy, and power are fundamental and interconnected concepts in physics
    • Work is done when a force (push or pull) applied to an object causes displacement
    • Energy is defined as the capacity to do work
    • Power is the rate at which work is done (work per unit time)

    Types of Energy

    • Mechanical energy, thermal energy, nuclear energy, chemical energy, electromagnetic energy, sonic energy, gravitational energy, kinetic energy, potential energy, ionization energy are examples of energy forms

    Work Done by a Constant Force

    • The work done by a constant force is calculated as the product of force magnitude, displacement magnitude, and the cosine of the angle between the force and displacement vectors

      • Formula: W = FΔr cos θ
      • θ is the angle between force (F) and displacement (Δr) vectors.

    • Forces that act perpendicular to the direction of motion do no work

      • Example: Normal force and gravitational force when object moves only horizontally

    Work Done by a Varying Force

    • When a force varies with position, the work done is the area under the force-displacement curve
      • Formula: W =∫xixf Fx dx

    Kinetic Energy and the Work-Kinetic Energy Theorem

    • Kinetic energy (KE) is the energy of motion (½mv²)
    • The net work done on an object equals the change in its kinetic energy
      • Formula: Wext = ΔK = Kf - Ki
    • If the net work is positive, the speed increases
    • If the net work is negative, the speed decreases

    Potential Energy of a System

    • Potential energy (PE) is energy stored in a system due to position or configuration
    • Gravitational potential energy (PEg): stores energy due to height or vertical position
      • Formula: PEg = mgh (m = mass, g = acceleration due to gravity, h = height)
    • Energy changes associated with conservative forces (e.g., gravity) are often expressed as potential energy

    Conservative and Nonconservative Forces

    • Conservative forces: do not dissipate energy from the system and are independent of the path taken
      • Examples: gravitational, electric, and elastic forces
    • Nonconservative forces: dissipate energy, dependent on the path taken
      • Example: friction, air resistance

    Examples (Specific problem details are included in the pages scanned)

    • Various examples illustrate the concepts using different situations and calculations

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    BAS 021 Physics I Chapter 4 Energy of a system v2 PDF

    Description

    This quiz covers fundamental concepts of work, energy, and power as presented in BAS 021 Physics I. Explore the details of work done by different forces, the work-kinetic energy theorem, and various types of energy. Test your understanding of how these concepts are interconnected in the realm of physics.

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