work and power
DESCRIPTION
Work and Power powerpoint presentationDiscussion and sample problemsTRANSCRIPT
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REVIEW
A boy pulls a wagon with a force of 6 N east as another boy pushes it with a force
of 4N east. What is the net force.
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REVIEW
What is the difference between balanced and
unbalanced forces?
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What is WORK? Select the activities below that
require the least amount of work.a) Carrying heavy books homeb) Reading a 300 page novelc) Lifting a 45kg massd) Holding a steel beam in place for 3 hre) Jacking up a car
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What is WORK? Work: using a force to move an object
a distance Both the force and the motion of the
object are in the same direction
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Work or Not?1. A scientist delivers a speech to an audience
of his peers. 2. A body builder lifts 350 pounds above his
head. 3. A mother carries her baby from room to
room. 4. A father pushes a baby in a carriage.5. A woman carries a 20 kg grocery bag to her
car?
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Which is work?
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What is WORK?Work is measured in Joules.
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ExamplesExample 1: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?
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ExamplesExample 2: A student lifts a box of books that weighs 200 N. The box is lifted 2.5 m. How much work does the student do on the box?
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ExamplesExample 3: If a man pushes a concrete block with 20 N of force and it does not move, how much work has he done?
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What is Power? Power: the rate at which work is done
Measured in watts
Power = work ÷ time
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ExamplesExample 4: A box that weighs 375 N is lifted a distance of 35.0 m straight up by a cable attached to a motor. The job is done in 5.0 seconds. What power is developed by the motor in watts?
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ExamplesExample 5: How much power will it take to move a 100 N mass a distance of 10 meters in 5 seconds?
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ExamplesExample 6: How much power will it take to move a 10 kg mass at an acceleration of 2 m/s/s a distance of 10 meters in 5 seconds? This problem requires you to use the formulas for force, work, and power all in the correct order.
Force = Mass x Acceleration Work = Force x Distance
Power = Work/Time
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ExamplesExample 7: Two physics students, Ben and Bonnie, are in the weightlifting room. Bonnie lifts the 50 kg barbell over her head (approximately .60 m) 10 times in one minute; Ben lifts the 50 kg barbell the same distance over his head 10 times in 10 seconds. Who did more work?
Work = Force x DistancePower = Work/Time
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ExamplesBen and Bonnie do the
same amount of work; they apply the same force to lift the same barbell the same distance above their heads.
Yet, Ben is the most powerful since he does the
same work in less time. Power and time are
inversely proportional.
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Exit slip1.How much work is done by a person who uses a force of 27.5N to move a grocery buggy 12.3m?
2. What is the difference between power and work?