1. ENGINEERING PHYSICS SEMESTER 2 2011/2012

2. ENGINEERING PHYSICS SUB-CHAPTERS: ● Work and standard units ● Power concept & Power Calculation ● Kinetic energy concept ● Potential Energy ● The law of conservation of energy SEMESTER 2 2011/2012

3. ENGINEERING PHYSICS ENERGY ● The ability to do work. When work is done, energy is transferred ● Forms of energy e.g. electrical, chemical heat, nuclear, mechanical etc ● Units: Joules (J) ● Types of energy – Kinetic – Potential ● Energy comes in many forms and always conserved. SEMESTER 2 2011/2012

4. ENGINEERING PHYSICS FORM of ENERGY SEMESTER 2 2011/2012

5. ENGINEERING PHYSICS Kinetic Energy Concept SEMESTER 2 2011/2012 Kinetic energy is the ability to do work through motion. Also called as energy of motion Remember Multiply both side with mass; Thus, kinetic energy; K = kinetic energy m= mass v = velocity vf = final velocity vo = initial velocity

6. ENGINEERING PHYSICS SEMESTER 2 2011/2012 The work done on a block by a constant force in moving it along a horizontal frictionless surface is equal to the change in the block’s kinetic energy: W = ΔK.

7. ENGINEERING PHYSICS Example SEMESTER 2 2011/2012 What is the kinetic energy of a 4 kg shot-put thrown by an athlete at a speed of 15 m/s? Solution: Kinetic energy, = ½ (4 kg)(15 m/s)(15 m/s) = 450 J

8. ENGINEERING PHYSICS Potential Energy SEMESTER 2 2011/2012 Potential energy exists whenever an object which has mass, has a position within a force field (gravitational, magnetic, electrical). An object having potential energy has potential to do work Often called the energy of position We will focus primarily on gravitational potential energy (energy an object has because of its height above the Earth)

9. ENGINEERING PHYSICS Gravitational Potential Energy SEMESTER 2 2011/2012 Gravitational potential energy U = mgy where m = mass g = acceleration due to gravity y =distance

10. ENGINEERING PHYSICS Kinetic & Potential Energy Relationship SEMESTER 2 2011/2012

11. ENGINEERING PHYSICS Example SEMESTER 2 2011/2012 What is the potential energy of a 12 kg mass raised to a height of 25 m? Solution Potential Energy = weight x height change Weight (m x g) = 12 kg x 9.8 N/kg = 117.6 N Height change, y = height at end - height at start = 25 - 0 = 25 m Potential energy (U) = m x g x y = 117.6 N x 25 m = 2940 J

12. ENGINEERING PHYSICS Example SEMESTER 2 2011/2012 A diver of 75 kg drops from a board 10.0 m above the water surface, as in the Figure. Find his speed 5.00m above the water surface. Neglect air resistance.

13. ENGINEERING PHYSICS The Law of Conservation of Energy SEMESTER 2 2011/2012 The Law of Conservation of Energy States: the total energy of an isolated system is always conserved Energy is neither created nor destroyed; it is converted from one form to another example in a nuclear power station. – Nuclear energy is converted into heat. – Heat boils water to steam – Heat in the steam is converted into kinetic energy in the turbines – Which is converted into electrical energy in the generator

14. ENGINEERING PHYSICS Conservative & Nonconservative Force SEMESTER 2 2011/2012

15. ENGINEERING PHYSICS Example SEMESTER 2 2011/2012 A skier with a mass of 80kg starts from rest at the top of a slope and skis down from an elevation of 110m. The speed of the skier at the bottom of the slope is 20m/s (a)Show that the system is nonconservative (b) How much work is done by the nonconservative force of friction