Work and Power 2

Terms

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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 500-N 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 1000-N 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

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