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Work and PowerWork and Power

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What is work?What is work?

DefinitionDefinition: energy transferred by a : energy transferred by a _____________ to move an object a _____________ to move an object a _____________ (when both the force _____________ (when both the force and the motion of the object are in and the motion of the object are in the same direction.)the same direction.)

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Work or Not?Work or Not?

According to the According to the scientific definition, scientific definition, what is work and what is work and what is not?what is not? a teacher lecturing a teacher lecturing

to her classto her class a mouse pushing a a mouse pushing a

piece of cheese piece of cheese with its nose across with its nose across the floorthe floor

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Work or Not?Work or Not?

According to the According to the scientific definition, scientific definition, what is work and what is work and what is not?what is not? a teacher lecturing a teacher lecturing

to her classto her class a mouse pushing a a mouse pushing a

piece of cheese piece of cheese with its nose across with its nose across the floorthe floor

Work or NotWork or Not

Why?Why?

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What’s work?What’s work? A scientist delivers a speech to an A scientist delivers a speech to an

audience of his peers. audience of his peers. A body builder lifts 350 pounds A body builder lifts 350 pounds

above his head. above his head. A mother carries her baby from room A mother carries her baby from room

to room. to room. A father pushes a baby in a carriage.A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag A woman carries a 20 kg grocery bag

to her car? to her car?

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What’s work?What’s work? A scientist delivers a speech to an A scientist delivers a speech to an

audience of his peers. audience of his peers. NoNo A body builder lifts 350 pounds A body builder lifts 350 pounds

above his head. above his head. YesYes A mother carries her baby from room A mother carries her baby from room

to room. to room. NoNo A father pushes a baby in a carriage. A father pushes a baby in a carriage. YesYes A woman carries a 20 km grocery A woman carries a 20 km grocery

bag to her car? bag to her car? NoNo

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Formula for workFormula for work

Work = _________ x DistanceWork = _________ x Distance The unit of work is newton x meters The unit of work is newton x meters One ____________ is equal to one One ____________ is equal to one

____________ So, the unit of work is a So, the unit of work is a ____________________

J= 1 N x m = 1 kg x mJ= 1 N x m = 1 kg x m22/s/s22

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W=FDW=FD

Work = Force x Work = Force x DistanceDistance

Calculate: If a Calculate: If a man pushes a man pushes a concrete block 10 concrete block 10 meters with a meters with a force of 20 N, force of 20 N, how much work how much work has he done?has he done?

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W=FDW=FD

Work = Force x Work = Force x DistanceDistance

Calculate: If a Calculate: If a man pushes a man pushes a concrete block 10 concrete block 10 meters with a meters with a force of 20 N, how force of 20 N, how much work has he much work has he done? done? 200 joules200 joules(W = 20N x 10m)(W = 20N x 10m)

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PowerPower Power is the __________ at which work Power is the __________ at which work

is done. is done.

Power = WorkPower = Work**/Time/Time

or P= W/tor P= W/t The unit of power is the watt.The unit of power is the watt.

1 watt= ______________1 watt= ______________

Work vs. PowerWork vs. Power

Work vs. Power

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Concept CheckConcept Check

1. Describe the difference between work 1. Describe the difference between work and power?and power?

2. How is work being done in the following 2. How is work being done in the following situationsituation

a.a. Powerlifting Powerlifting

b.b. Dropping your textbookDropping your textbook

c.c. Doing a handstandDoing a handstand What is the unit for lightbulbs? Why is that What is the unit for lightbulbs? Why is that

unit used?unit used?1313

Math PracticeMath Practice

1. A crane use an average force of 5300 N to lift 1. A crane use an average force of 5300 N to lift a girder 25 m. How much work does the crane a girder 25 m. How much work does the crane do on the girder?do on the girder?

2. Aylssa powerlifts Kyle over her head 1 m with 2. Aylssa powerlifts Kyle over her head 1 m with a force of 250 N. How much work was done?a force of 250 N. How much work was done?

3. While rowing in a race, John uses his arms 3. While rowing in a race, John uses his arms to exert a force of 165 N per stroke while pulling to exert a force of 165 N per stroke while pulling the oar 0.800 m. How much work does he do in the oar 0.800 m. How much work does he do in 30 strokes?30 strokes?

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Math PracticeMath Practice

4. While rowing in a race, John does 3960 J of work on 4. While rowing in a race, John does 3960 J of work on the oars in 60.0 s. What is his output in watts.the oars in 60.0 s. What is his output in watts.

5. Steve using a jack does 4320 J of work to lift a car 5. Steve using a jack does 4320 J of work to lift a car 1.5 m in 100.0 s. What is the power output?1.5 m in 100.0 s. What is the power output?

6. Mr. Farrell walks up the stairs on his way to make 6. Mr. Farrell walks up the stairs on his way to make copies. He weight 622 Newtons and the stairs go 5.75 copies. He weight 622 Newtons and the stairs go 5.75 vertically.vertically.

a. Calculate my output if I climb the stairs in 8.9s.a. Calculate my output if I climb the stairs in 8.9s.

b. What is I climb the stairs in 7.2 s?b. What is I climb the stairs in 7.2 s?

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