Potential and Kinetic Energy…

• kinetic energy: is the energy which an object possesses due to its motion

• Potential energy: energy stored in a system because of its position.

http://www.youtube.com/watch?v=qZ4FFWvZtyo

Potential Energy

• Potential Energy is it has the ability to do work because of position or state.

• The energy of an object due to its position above the surface of the Earth.

Ep = W Potential energy equal to work done!

Ep = Fd

Gravitational Potential Energy

pE mghhttp://www.youtube.com/watch?v=DMrnAcnsvKY

Example

• Change in gravitational potential energy depends only on change in vertical height.

Elastic Potential Energy• The energy from a spring being altered from

its standard shape.

k: spring constantx: distance spring is stretched or compressed.

21

2pE kx

http://www.youtube.com/watch?v=Jnj8mc04r9E

Example 2An apple of mass 0.10 kg is suspended from a vertical

spring with spring constant 9.6 N/m. How much elastic potential energy is stored in the spring if the apple stretches the spring 20.4 cm?

?

:

204.0

6.9

:

e

mN

E

Unknown

mx

k

Givens

Example 2

An apple of mass 0.10 kg is suspended from a vertical spring with spring constant 9.6 N/m. How much elastic potential energy is stored in the spring if the apple stretches the spring 20.4 cm?

?

:

204.0

6.9

:

e

mN

E

Unknown

mx

k

Givens JE

mESolve

kxESelect

e

mN

e

e

20.0

204.06.9:

:2

21

221

Example 2

An apple of mass 0.10 kg is suspended from a vertical spring with spring constant 9.6 N/m. How much elastic potential energy is stored in the spring if the apple stretches the spring 20.4 cm?

?

:

204.0

6.9

:

e

mN

E

Unknown

mx

k

Givens

JE

mESolve

kxESelect

e

mN

e

e

20.0

204.06.9:

:2

21

221

Example 2 Follow-Up

How much gravitational potential energy did the apple lose?

Example 2 Follow-Up

How much gravitational potential energy did the apple lose?

?

:

204.0

8.9

10.0

:

2

g

sm

E

Unknown

mh

g

kgm

Givens

Example 2 Follow-Up

How much gravitational potential energy did the apple lose?

?

:

204.0

8.9

10.0

:

2

g

sm

E

Unknown

mh

g

kgm

Givens

JE

mkgESolve

hmgESelect

g

sm

g

g

20.0

204.08.910.0:

:

2

Example 2 Follow-Up

How much gravitational potential energy did the apple lose?

?

:

204.0

8.9

10.0

:

2

g

sm

E

Unknown

mh

g

kgm

Givens

JE

mkgESolve

hmgESelect

g

sm

g

g

20.0

204.08.910.0:

:

2

• Pg. 178– # 1-9

Kinetic Energy

21

2kE mv

• The energy due to the motion of an object• A scalar quantity

http://www.youtube.com/watch?v=BGmUVoX5s58

begin at 43sec

• A 0.300kg ball is pushed horizontally at a velocity of 20.0 m/s N. What the Ek of the ball as it moves?

• The kinetic energy of a moving object is 950 J as it moves 14.2 m/s. What is its mass?

Example 6.5

• On a highway, a car with mass of 1200kg and a Ek of 2500 J. What must the velocity of the car be?

Practice

• Pg. 179– # 4-5

• Pg. 181– # 6-7

• Pg. 182– #1-3, 5-7,