1. Work & Energy Chapter 5

2. What is energy? The property of an object that allows it to produce a change in itself or its environment. The property of an object that allows it to produce a change in itself or its environment. In this class we will study In this class we will study Work Work Gravitational Potential Energy Gravitational Potential Energy Kinetic Energy Kinetic Energy Spring Potential Energy Spring Potential Energy

3. Work W = Fdcosθ W = Fdcosθ Unless explicitly told otherwise, assume that the angle between force and displacement is 0. Unless explicitly told otherwise, assume that the angle between force and displacement is 0. When θ=90 o, cosθ=0 so no work is done. When θ=90 o, cosθ=0 so no work is done. Generic term for energy given to an object from an outside source or energy lost to the outside from an object. Generic term for energy given to an object from an outside source or energy lost to the outside from an object. So Work is a change in energy So Work is a change in energy d

4. Work Unit for energy is the Joule. Unit for energy is the Joule. Other units: calories, kilowatt hours, Other units: calories, kilowatt hours, Negative work means that the object in question is losing energy i.e. friction. Negative work means that the object in question is losing energy i.e. friction. Sometimes labeled Q when referring to heat specifically. Sometimes labeled Q when referring to heat specifically.

5. Example #1 A crate is pulled 5 m along a floor by a 100 N horizontal force. What is the work done by that applied force?

6. Example #2 This time the crate gets pulled by the 100 N force but at 25  angle over the same 5 m distance. What work is done by the applied force this time?

7. Example #3 A 10 kg box is pulled 15 m by 200 N of force at 0 deg. The coefficient of friction between the box and the floor is 0.65. Find the work done by F A, f, gravity, and F N. What is the total work done by the person pulling the box?

8. Example #4 Joe Schmo (80 kg) carries an 8 kg package up the steps to the second floor which is 4 m in height. The length of the staircase is 5 m. A) What is the work done by Joe on the box? B)What is the work done by Joe?

9. Power The rate at which energy is transferred. The rate at which energy is transferred. Unit is a Watt Unit is a Watt 1W=1J/s, so 1J=1Ws and we can convert from Joules to kWhr. 1W=1J/s, so 1J=1Ws and we can convert from Joules to kWhr. English unit is horsepower. English unit is horsepower.

10. Example #5 You leave the 65W bulb in your room on for two weeks. How much energy does it use? You leave the 65W bulb in your room on for two weeks. How much energy does it use? If the electric company charges 12.5 cents per kilowatt hour, how much does it cost your parents? If the electric company charges 12.5 cents per kilowatt hour, how much does it cost your parents?