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Class 11 Physics Ch-5: Work, Energy and Power Notes
Class 11 Physics Chapter 5 Work, Energy and Power explains the concepts of work done by a force, kinetic and potential energy, the work-energy theorem, conservation of mechanical energy, and power.
Overview of Topics & Subtopics
Important Questions and Answers
Q1: Define work done by a constant force and state the condition for zero work.
Answer: Work done by a constant force is defined as W = F·d·cosθ, where F is the force, d is the displacement, and θ is the angle between the force and displacement vectors. Work done is zero when the force is perpendicular to the displacement (θ = 90°), or when there is no displacement, or when the force itself is zero.
Q2: State the work-energy theorem.
Answer: The work-energy theorem states that the total work done by all forces acting on an object equals the change in its kinetic energy, i.e., W = ΔKE = (1/2)mv² − (1/2)mu², where u and v are the initial and final speeds respectively.
Q3: What is the law of conservation of mechanical energy?
Answer: The law of conservation of mechanical energy states that in the absence of non-conservative forces like friction, the total mechanical energy (sum of kinetic and potential energy) of an isolated system remains constant, though energy may convert between kinetic and potential forms.
Q4: Differentiate between elastic and inelastic collisions.
Answer: In an elastic collision, both momentum and kinetic energy of the system are conserved. In an inelastic collision, momentum is conserved, but kinetic energy is not conserved as some of it is converted into other forms of energy such as heat, sound, or deformation.
Q5: Define power and give its SI unit.
Answer: Power is defined as the rate at which work is done or energy is transferred, given by P = W/t. Its SI unit is the watt (W), where 1 watt equals 1 joule of work done per second.
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