1. Work, Energy, Power

2. Chapter objectives
Use the principle of conservation of mechanical energy and the work-energy principle to solve problems about a moving particle
Solve problems about a moving vehicle including calculating the power developed by its engine

3. WORK 3.1

10. 8g F P
30º R

11. 8g F P
30º R

12. Forces at an angle to the direction of motion
For a force at an angle to the direction of motion:
Work done = component of force in direction of motion x distance moved in the same direction.

13. A sledge is pulled across a smooth horizontal floor by a force of magnitude 50 N inclined at 35° to the horizontal. Find the work done by the force in moving the packing case a distance of 23m

14. The kinetic energy of a mass m moving at a velocity v is
The kinetic energy of a body is the energy that it possesses by virtue of its motion. When a force acts on a body to increase its speed, then the work done equates to the increase in kinetic energy of the body (provided that no other forces are involved)
The kinetic energy of a mass m moving at a velocity v is

21. The important thing to remember is that potential energy changes after a change in height. The 5.5m displacement is not the value of h.

23. Conservation of Energy 3.3
Consider the situation of a moving body where no work is done against friction and that gravity is the only other force present then:
Total Energy = Kinetic Energy + Potential Energy = Constant
Or in other terms:
Total Initial Energy = Total Final Energy

24. Let the distance travelled be z m.

27. A ball of mass 1.5kg is projected up a rough plane inclined at an angle of 30º to the horizontal with a speed of 4 ms-1. Given that the coefficient of friction between the particle and the plane is 0.2 find the distance the particle moves up the plane before coming to rest.

34. Power 3.4
Power is a measure of the rate at which work is being done. The unit of work is the Watt. If 1 Joule of work is done in 1 second then the rate of work is 1 Watt.
Power = Force × Distance moved in one second or
Power = Force × Velocity

41. The End