1. Warm up 1. A 500 kg car is traveling 18 m/s, how much kinetic energy does it have (in Joules)? 1. A 500 kg car is traveling 18 m/s, how much kinetic energy does it have (in Joules)? 2. A 4 kg mutant rat has a velocity of -10 m/s. 2. A 4 kg mutant rat has a velocity of -10 m/s. A) How much kinetic energy does it have? A) How much kinetic energy does it have? B) What does the negative sign mean? B) What does the negative sign mean?

2. Practice 1. A 7 kg bird is flying at 15 m/s, what is the bird’s kinetic energy? 1. A 7 kg bird is flying at 15 m/s, what is the bird’s kinetic energy? 2. A 2000 kg car is traveling at 13 m/s, what is the car’s kinetic energy? 2. A 2000 kg car is traveling at 13 m/s, what is the car’s kinetic energy? 3. A 400 kg emu goes from traveling 3 m/s to 7 m/s, what is the change in the ostrich’s kinetic energy? 3. A 400 kg emu goes from traveling 3 m/s to 7 m/s, what is the change in the ostrich’s kinetic energy? 4. If a 9 kg object has 400 J of work done on it. How much will its velocity change? 4. If a 9 kg object has 400 J of work done on it. How much will its velocity change?

3. Potential Energy Potential is energy that is stored Potential is energy that is stored Not being used yet. Not being used yet. Abbreviated “U” Abbreviated “U” Unit is also the Joule (J) Unit is also the Joule (J) There are a few main ways to store energy There are a few main ways to store energy By position (Gravitational) By position (Gravitational) By configuration (Elastic) By configuration (Elastic) By substance (Chemical [Think gasoline]) By substance (Chemical [Think gasoline])

4. Gravitational PE Energy stored by position Energy stored by position Think of a sled at the top of a hill Think of a sled at the top of a hill Or a boulder that is teetering Or a boulder that is teetering Gravitational Potential Energy = mgh Gravitational Potential Energy = mgh m = mass m = mass g = 9.8 m/s 2 g = 9.8 m/s 2 h = height (in m) h = height (in m)

5. Examples How much gravitational potential energy does a 10 kg object suspended 3 m off the ground have? How much gravitational potential energy does a 10 kg object suspended 3 m off the ground have? How much gravitational potential energy does a 6 kg object suspended 9 m off the ground have? How much gravitational potential energy does a 6 kg object suspended 9 m off the ground have?

6. Practice What is the potential energy of a 200 kg car at the top of a ramp if it is 30 m above level ground? What is the potential energy of a 200 kg car at the top of a ramp if it is 30 m above level ground? What is the potential energy of a 3 kg bob at the end of a pendulum when it is 0.3 m above its lowest point? What is the potential energy of a 3 kg bob at the end of a pendulum when it is 0.3 m above its lowest point?

7. Elastic PE Energy stored by position in a spring Energy stored by position in a spring Think Bungee cords or springs Think Bungee cords or springs Elastic Potential energy = ½ kx 2 Elastic Potential energy = ½ kx 2 k = spring constant k = spring constant x = displacement from rest position x = displacement from rest position

8. How much elastic potential energy is in a spring displaced.25 m from rest when k = 2? How much elastic potential energy is in a spring displaced.25 m from rest when k = 2? If 4 J of work displaces a spring by 0.4 m, what is the spring constant? If 4 J of work displaces a spring by 0.4 m, what is the spring constant?

9. How much elastic potential energy is in a spring displaced.15 m from rest when k = 6? How much elastic potential energy is in a spring displaced.15 m from rest when k = 6? If 12 J of work displaces a spring by 0.6 m, what is the spring constant? If 12 J of work displaces a spring by 0.6 m, what is the spring constant?

10. Homework pg 267 pg 267 (4, 28, 29, 44-47, 49) (4, 28, 29, 44-47, 49)