Do Now:

Determine the change in potential energy if a 3 kg box is raised from a height of 1 m to a height of 3 m.

Do Now:

Complete the Warm-up Activity sheet

A force of 56 N is applied to a box at an angle of 41˚. If the box moves a distance of 0.23 m, what is the work done on the box?

Do Now (2/1/12):

CONSERVATION OF ENERGY

2/2/11

What is conservation of mass?

Conservation of Energy:

Energy cannot be created or destroyed. The total amount of energy in a system is conserved over time.

Conservation of Energy

PEKEEtotal

Rollercoaster

http://www.physicsclassroom.com/mmedia/energy/ce.cfm

Example:

1. What is the total energy at each given point?2. Which type of energy gets larger as the skier falls?3. Which type of energy gets smaller as the skier

falls?

Do Now (2/2/12):

A 100 kg car on a rollercoaster begins 60 m above the ground.

1. What is the car’s potential energy at the top?

2. What is the car’s total energy at the top?3. What is the car’s total energy at the bottom?4. What type of energy is equivalent to the

total energy at the bottom?

*if you weren’t here yesterday, please just write the questions!

Review: Conservation of Energy:

Energy cannot be created or destroyed. The total amount of energy in a system is conserved over time.

Review: Conservation of Energy

PEKEEtotal

Strategies for solving Energy problems

Calculate the total energy E as soon as possible

The PE at the reference level is 0 – therefore at the reference level:

At the top PE is a maximum – therefore KE is 0 and

KEEtotal

PEEtotal

Practice!

Use the rest of class to practice Conservation of Energy

LAB!

Read over the lab and fill out #’s 1 and 5 on the Results/Calculations sheet

Do Now:

You lift a 2 kg textbook from the floor to shelf 2.1 m above the floor.

1. What is the book’s gravitational potential energy relative to the floor?

2. What is its gravitational energy relative to your head, assuming you’re 1.65 m tall?

Do Now (2/3/12):

In this unit, we learned the food is a form of stored energy. How many M&M candies do you think you would need to replace the energy you’d burn if you climbed the steps from the ground floor to the third floor?

LAB!

Read over the lab and fill out #’s 1 and 5 on the Results/Calculations sheet

ONE person from each group will get the hall pass at a time.

1. Count the stairs2. Measure the height per stair3. One person at a time climbs the stairs

and times themselves 4. Everyone else in the classroom should

be working on calculations

LAB! Factor label conversion

To find the energy in EACH candy

Jcal

J

tbsp

cal

MM

tbspMMEcandy ____

1

4190

1

55

&15

1&1

candy

g

E

UCandies

#

Strategies for solving Energy problems

Calculate the total energy E as soon as possible

The PE at the reference level is 0 – therefore at the reference level:

At the top PE is a maximum – therefore KE is 0 and

KEEtotal

PEEtotal

Practice:

Take 15 min to work on Practice Problems #5-7 on p. 254 in your classroom textbook. We will go over them at the end of class.

Example: Conservation of EnergyA 10 kg ball is dropped from a cliff 50 m

tall.1. What is the ball’s potential energy

before being dropped?2. What is the ball’s total energy before

being dropped?

Example: Conservation of EnergyA 10 kg ball is dropped from a cliff 50 m

tall.3. At a height of 30 m, what is the kinetic

energy of the ball?

Example: Conservation of EnergyA 10 kg ball is dropped from a cliff 50 m

tall.4. When it reaches of velocity of 20 m/s,

what is the potential energy?

Do Now (2/6/12):

A 10 kg ball is dropped from a 50 m cliff.

1. What is the potential energy at the top?

2. What is the work done?3. What is the kinetic energy at

the bottom?4. What is the velocity of the

stone right before it hits the ground?

Reminders:

TUESDAY 2/7/12 is the LAST DAY to MAKE UP QUIZZES. Quizzes not made up by then will be filled in with a score of zero.

Keep your homework for another night; use your Conservation of Energy sheet to make a NOTECARD for tomorrow’s quiz.

Energy and Power LABS are due tomorrow

Popper Lab

Use TWO HANDS to carry the balances

Raise your hand if you have any QUESTIONS

DO NOT LOSE YOUR POPPER!!!!!!!!!!!! This will result in a grade deduction.

Do Now (2/7/12):

1. In our popper lab yesterday, what form of energy does the popper have before it pops?

2. What was the popper’s initial source of energy?

3. Was mechanical energy conserved throughout the motion of the popper?

4. What happened to the energy after the popper stopped moving?

Pass in:

Homework

Labs

Practice:

Use the rest of class to work on “Conservation of Energy”

On #2 cross off “weighs 20 N”

Do Now:

A 15 kg ball is dropped from rest with a potential energy of 4600 J. What is the potential energy when the velocity is 12 m/s?