Work and Power 2
Terms
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copy deck
 What is the formula for a joule?

A joule equals one newton x one meter
(N x m)  What is the result of a force moving an object over a distance?
 Work
 What are you doing when you push, lift, or throw and object?
 Work
 What is the formula for work?
 W = F x D
 What is "F" ?
 F = force acting on an object
 What is "d"?
 d = distance the object moves in the direction of the force
 What is the unit of measurement for work in the metric system?
 Joule
 A joule equals the force of what?
 A newton moving an object 1 meter
 Who is the joule named after?

James Prescott Joule
19th century English physicist who studied transformation  What is the work done when a 500N student climbs a rope for 5 meters?

W = F x D
W = 500n x 5m
W = 2500 x m
W = 2500J  Is a horse doing work when it stands with a rider sitting on it?
 No  because the horse is not pushing, lifting, or throwing. No force is acting over a distance.
 When you climb to the top of rope and hang there, are you doing work?
 No  not moving your body over a distance
 What is the amount of work done during a given period of time
 Power
 How is power measured?
 Power is measured in watts (W)
 A watt is equal to how many joule?

1 W = joule per second
(J/s)  How many joules is a 100W lightbulb using?
 100 joules per second
 A kilowatt (kW) is equal to how many watts?
 1 kW = 1000 W
 One horsepower is equal to how many watts?
 1 hp = 0.746W
 Horsepower is used to describe what?
 The power of engines
 Who described the power of a steam engine?

James Watt
A Scottish engineer described the power used to a horse to pull a heavy load  What is the equation of power?

Power = Work/Time
P = w/t  What is the power of a motor that does 2000 J of work in a 10 second period?

P = w/t
P = 2000J/10s
P = 200J/S
P = 200W  If the power of a motor is 200W, what is the horsepower of the motor?
 200W / 746W = .26hp
 Is throwing a football 20 yards work or not?
 Yes
 You push against a wall until you are tired. Is this work?
 No
 Your study these flashcards all day long for this stupid test. Is this work?
 No
 You push your brother out of your way to sit down  are you working?
 Yes
 How much work is done when a 175 N man pulls a sled 500m?

W = F x D
W = 175 x 500
W = 87,500J  A 98 N woman carries her baby 12 m. How much work is done?
 No work
 What is the work done when a 1000N person jumps 1 meter into the air?

W = F x D
W = 1000 N x 1m
W = 1000 x m
W = 1000J 
A 100W lightbulb has more what than a 60W bulb?
a. power
b. joule
c. watt
d. force  Power
 What is the amount of work per unit of time?
 Power
 What is the reate at which work is done?
 Power
 When power increases, does the rate of work increase or decrease
 Increase
 How much work does a 150w lightbulb do?
 150 joules
 Power is force x distance and divided by what?
 Time
 When time and force remain the same, power is increased when what increases?
 Distance
 What is the equation for power?
 P = Work/Time
 Power is measured in what?
 watts
 One horsepower equals how many watts?
 746 watts
 A pencil sharpener uses 1,000 joules in 10 seconds. What is the power usage?

P = 1,000j /10s
P = 100j / s
P = 100W