Tuesday, September 29, 2009Tuesday, September 29, 2009

In olden days, something was only considered In olden days, something was only considered “doing work” if you were getting tired or sweaty “doing work” if you were getting tired or sweaty doing it. Make up a definition for this type of doing it. Make up a definition for this type of work using what we know about energy (use the work using what we know about energy (use the word energy)word energy)

HW: Read 6.1 in your book, answer 3 questionsHW: Read 6.1 in your book, answer 3 questions

Read 6.4, answer 3 questionsRead 6.4, answer 3 questions

Read 6.5, answer 3 questionsRead 6.5, answer 3 questions

As an object falls, its potential As an object falls, its potential energy decreases. What happens energy decreases. What happens

to its kinetic energy?to its kinetic energy?

It a

lso d

ecre

a...

It in

crea

ses

It re

mai

ns th

e...

0% 0%0%

1.1. It also decreasesIt also decreases

2.2. It increasesIt increases

3.3. It remains the It remains the samesame

To determine potential energy of To determine potential energy of an object due to gravity, you an object due to gravity, you need which of the following?need which of the following?

Hei

ght

Forc

e

Wei

ght

0% 0%0%

1.1. HeightHeight

2.2. ForceForce

3.3. WeightWeight

If we double the velocity of an If we double the velocity of an object, what happens to its object, what happens to its

kinetic energy?kinetic energy?

It a

lso d

ouble

...

It q

uadru

ples

It tr

iple

s

It re

mai

ns th

e...

0% 0%0%0%

1.1. It also doublesIt also doubles

2.2. It quadruplesIt quadruples

3.3. It triplesIt triples

4.4. It remains the It remains the samesame

WorkTwo things needed for work to be done:1. The application of a force2. The movement of something by that force

Work = force x distance

FdW

What is needed to do twice the work?

5 m

12 N

Work

Work = force x distance

FdW

What is needed to do twice the work?

Work

Work = force x distance

FdW

The unit of measurement for work combines force and distance.

The newton-meter (N*m) or joule.

An athlete lifts a 1.0-Newton weight An athlete lifts a 1.0-Newton weight 2.00 meters. How much work did 2.00 meters. How much work did

they do?they do?

2.0

Wat

ts

2.0

Joules

1.0

Wat

ts

1.0

Joules

4.0

Wat

ts

4.0

Joules

.5 W

atts

.5 Jo

ules

12% 12% 12% 12%12%12%12%12%1.1. 2.0 Watts2.0 Watts2.2. 2.0 Joules2.0 Joules3.3. 1.0 Watts1.0 Watts4.4. 1.0 Joules1.0 Joules5.5. 4.0 Watts4.0 Watts6.6. 4.0 Joules4.0 Joules7.7. .5 Watts.5 Watts8.8. .5 Joules.5 Joules

An object with a weight of 2.00 N An object with a weight of 2.00 N falls from a cliff that is 35.0 ft? falls from a cliff that is 35.0 ft? Calculate its potential energy.Calculate its potential energy.

720

J

686

J

70.

0 J

6.8

6 J

25% 25%25%25%

1.1. 720 J720 J

2.2. 686 J686 J

3.3. 70.0 J70.0 J

4.4. 6.86 J6.86 J

An object with a mass of 3.00 kg An object with a mass of 3.00 kg falls from a cliff that is 40.0 m? falls from a cliff that is 40.0 m? Calculate its potential energy.Calculate its potential energy.

117

6 J

120

J

120

0 J

0% 0%0%

1.1. 1176 J1176 J

2.2. 120 J120 J

3.3. 1200 J1200 J

An object with a mass of 20.00 An object with a mass of 20.00 kg is speeding at 40.0 m/s? kg is speeding at 40.0 m/s? Calculate its kinetic energy.Calculate its kinetic energy.

400

J

320

00 J

160

00 J

0% 0%0%

1.1. 400 J400 J

2.2. 32000 J32000 J

3.3. 16000 J16000 J

An object with a mass of 62.5 kg An object with a mass of 62.5 kg is speeding at 22 m/s? Calculate is speeding at 22 m/s? Calculate

its kinetic energy.its kinetic energy.

151

25 J

687

.5 J

302

50 J

0% 0%0%

1.1. 15125 J15125 J

2.2. 687.5 J687.5 J

3.3. 30250 J30250 J

PowerPower

Power is the rate at which work is done.Power is the rate at which work is done. Unit of power: joule per second or Unit of power: joule per second or wattwatt..

interval timedonework

power

• One watt (W) is expended when one joule of work is done over one second.

• Kilowatt (kW) = 1000 watts• Megawatt (MW)= 1,000,000 watts• 1 hp = .75 kW 134 hp = 100 kW