Warm upWarm up

1. A 500 kg car is traveling 18 m/s, 1. A 500 kg car is traveling 18 m/s, how much kinetic energy does it how much kinetic energy does it have (in Joules)?have (in Joules)?

2. A 4 kg mutant rat has a velocity of 2. A 4 kg mutant rat has a velocity of -10 m/s.-10 m/s. A) How much kinetic energy does it A) How much kinetic energy does it

have?have? B) What does the negative sign mean?B) What does the negative sign mean?

PracticePractice

1. A 7 kg bird is flying at 15 m/s, what 1. A 7 kg bird is flying at 15 m/s, what is the bird’s kinetic energy?is the bird’s kinetic energy?

2. A 2000 kg car is traveling at 13 m/s, 2. A 2000 kg car is traveling at 13 m/s, what is the car’s kinetic energy?what is the car’s kinetic energy?

3. A 400 kg emu goes from traveling 3 3. A 400 kg emu goes from traveling 3 m/s to 7 m/s, what is the change in m/s to 7 m/s, what is the change in the ostrich’s kinetic energy?the ostrich’s kinetic energy?

4. If a 9 kg object has 400 J of work 4. If a 9 kg object has 400 J of work done on it. How much will its velocity done on it. How much will its velocity change?change?

Potential EnergyPotential Energy

Potential is energy that is storedPotential 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 There are a few main ways to store

energyenergy By position (Gravitational)By position (Gravitational) By configuration (Elastic)By configuration (Elastic) By substance (Chemical [Think gasoline])By substance (Chemical [Think gasoline])

Gravitational PEGravitational PE

Energy stored by position Energy stored by position Think of a sled at the top of a hillThink of a sled at the top of a hill Or a boulder that is teeteringOr a boulder that is teetering

Gravitational Potential EnergyGravitational Potential Energy = mgh = mgh m = massm = mass g = 9.8 m/sg = 9.8 m/s22

h = height (in m)h = height (in m)

ExamplesExamples

How much gravitational potential How much gravitational potential energy does a 10 kg object energy does a 10 kg object suspended 3 m off the ground have?suspended 3 m off the ground have?

How much gravitational potential How much gravitational potential energy does a 6 kg object suspended energy does a 6 kg object suspended 9 m off the ground have?9 m off the ground have?

PracticePractice

What is the potential energy of a 200 What is the potential energy of a 200 kg car at the top of a ramp if it is 30 kg car at the top of a ramp if it is 30 m above level ground?m above level ground?

What is the potential energy of a 3 What is the potential energy of a 3 kg bob at the end of a pendulum kg bob at the end of a pendulum when it is 0.3 m above its lowest when it is 0.3 m above its lowest point?point?

Elastic PEElastic PE

Energy stored by position in a springEnergy stored by position in a spring Think Bungee cords or springsThink Bungee cords or springs

Elastic Potential energyElastic Potential energy = ½ kx = ½ kx22 k = spring constantk = spring constant x = displacement from rest positionx = displacement from rest position

How much elastic potential energy is How much elastic potential energy is in a spring displaced .25 m from rest in a spring displaced .25 m from rest when k = 2?when k = 2?

If 4 J of work displaces a spring by If 4 J of work displaces a spring by 0.4 m, what is the spring constant?0.4 m, what is the spring constant?

How much elastic potential energy is How much elastic potential energy is in a spring displaced .15 m from rest in a spring displaced .15 m from rest when k = 6?when k = 6?

If 12 J of work displaces a spring by If 12 J of work displaces a spring by 0.6 m, what is the spring constant?0.6 m, what is the spring constant?

HomeworkHomework

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