[PHY] Chapter 7 - Work, Energy, Power

DARRELL ER (COPYRIGHTED) © TOPIC 7: WORK, ENERGY, POWER DARRELL ER (COPYRIGHTED) ©

CHAPTER ANALYSIS THE ABOUT MASTERY EXAM WEIGHTAGE DARRELL ER (COPYRIGHTED) ©

ENERGY KINETIC ENERGY & GRAVITATIONAL POTENTIAL ENERY WORK DONE KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

ENERGY ENERGY Energy is defined as the capacity to do work. Unit: Joule (J) Energy is a scalar quantity. DARRELL ER (COPYRIGHTED) ©

PRINCIPLE OF CONSERVATION OF ENERGY Kinetic Energy Kinetic energy is defined as the energy a body possesses due to its motion. Formula: Kinetic energy is directly proportional to mass and velocity squared. Gravitational Potential Energy Gravitational potential energy is the energy possessed by a body due to its position within a gravitational field. Formula: Gravitational potential energy is directly proportional to mass and height of object. DARRELL ER (COPYRIGHTED) © Principle of Conservation of Energy The principle of conservation of energy states that energy cannot be created or destroyed but can only change from one form to another or transferred from one body to another but the total amount of energy in the system is always constant. KE = mv2 1 2 GPE = mgh

WORK DONE WORK DONE Work done is defined as the product of the force and the distance moved in the direction of the force. Units: Joule (J) or Nm Formula: Work Done = F x d Work done can also be understood as the amount of energy that has been converted from one form to another or transferred from one body to another. Example For the box to move up the slope, there is work done to overcome friction. Work Done against friction = F x d = 3N x 5m =15 J The box also gained gravitational potential energy. This gain in energy is also work done as somebody had to exert energy to move the box to its new position. Gain in GPE = mgh = 1 x 10 x 3 = 30 J DARRELL ER (COPYRIGHTED) © Work done & energy has the same units, Joules (J). The best way to understand their relationship is: “We use energy to get work done” 4m 3m 5m Friction: 3N Mass: 1 kg

POWER EFFICIENCY KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

POWER POWER Power is defined as rate of doing work or the rate at which energy changes from one form to another. Units: watt (W) Formula: Example Work Done against friction = F x d = 3N x 5m =15 J Gain in GPE = mgh = 1 x 10 x 3 = 30 J Total work done = 45 J If the entire process took 10s, P = Work Done / time = 45J / 10s = 4.5 W DARRELL ER (COPYRIGHTED) © 4m 3m 5m Friction: 3N Mass: 1 kg Efficiency Efficiency is defined as the ratio of useful energy output to total energy input. Formula: *Note that no system in the world is 100% efficient! Efficiency = x 100% Useful output Total output