Work done, Energy and Power JPJC Notes

1 JURONG PIONEER JUNIOR COLLEGE 9749 H2 PHYSICS WORK, ENERGY AND POWER Content  Work  Energy conversion and conservation  Efficiency  Potential energy and kinetic energy  Power Learning Outcomes Candidates should be able to: (a) define and use work done by a force as the product of the force and displacement in the direction of the force (b) calculate the work done in a number of situations including the work done by a gas which is expanding against a constant external pressure: W p V (c) give examples of energy in different forms, its conversion and conservation, and apply the principle of energy conservation (d) show an appreciation for the implications of energy losses in practical devices and use the concept of efficiency to solve problems (e) derive, from the equations for uniformly accelerated motion in a straight line, the equation Ek = ½ mv2 (f) recall and use the equation Ek = ½ mv2 (g) distinguish between gravitational potential energy, electric potential energy and elastic potential energy (h) deduce that the elastic potential energy in a deformed material is related to the area under the force-extension graph (i) show an understanding of and use the relationship between force and potential energy in a uniform field to solve problems (j) derive, from the defini tion of work done by a force , the equation Ep = mgh for gravitational potential energy changes near the Earth’s surface (k) recall and use the equation Ep = mgh for gravitational potential energy changes near the Earth’s surface (l) define power as work done per unit time and derive power as the product of a force and velocity in the direction of the force

2 Introduction This topic involves the core ideas of Conservation Laws as well as Systems and Interactions. The concept of energy is one of the most important concepts in Science. Energy is present in various forms. The transformation of energy from one form to another and its conservation are essential in the study of physics. The concept of work links energy and force. Work is a means of transferring energy through application of a force. The concepts of work and energy can be applied to the dynamics of a mechanical system without resorting to Newton’s laws. Beyond mechanics, this approach can be applied in a wide range of phenomena in electromagnetism, thermal and nuclear physics. In addition, the energy approach often provides a simpler analysis than direct application of Newton’s laws because (1) energy is a scalar whereas force is a vector, and (2) only the initial and final states of a situation need to be considered without involving the intermediate processes. 1 Work (a) define and use work done by a force as the product of the force and displacement in the direction of the force 1.1 Definition of Work 1.2 Work don