work, power, and energy...power the rate at which work is done the rate of energy transfer power...
TRANSCRIPT
![Page 1: Work, Power, and Energy...Power The rate at which work is done The rate of energy transfer Power measures how quicklywork is done Units: Watts 1 Watt = 1 Joule per second π= ππ](https://reader033.vdocument.in/reader033/viewer/2022050405/5f822e34ecfcfa16307ff1e3/html5/thumbnails/1.jpg)
Work, Power, and Energy
Honors Physics
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Work
Work changes an objectβs energy
This is a dot product, meaningβ¦
W= πΉππππ (if there is an angle between F and d)
Units: Joules
1 Nm = 1 Joule
π = ΰ΄±πΉ β ΰ΄±π
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Example
A 50 kg crate is dragged along a floor for 5 meters with a force of 60 N. The rope makes an angle of 30 above the horizontal. How much work was done on it by the applied force?
a) 0 N
b) 250 N
c) 260 N
d) 300 N
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Power
The rate at which work is done
The rate of energy transfer
Power measures how quickly
work is done
Units: Watts
1 Watt = 1 Joule per second
π =ππππ
π‘
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Example
A crane lifts a 900 kg car vertically upward at a constant speed to a height of 15 meters in 45 seconds.
a) How much work is done on the car?
b) Calculate the power output of the motor.
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Example
A 40-kilogram student runs up a staircase to a floor that is 5.0 meters higher than her starting point in 7.0 seconds. The studentβs power output is
a) 29 W
b) 280 W
c) 1.4 Γ 103 W
d) 1.4 Γ 104 W
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Potential Energy
ππΈ = ππβ
Generally, potential energy is the energy an object has by virtue of its position in a system
Gravitational potential energy is a result of an objectβs height above Earth
A result of the work done to lift an object against gravity
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Kinetic Energy
The energy an object has by virtue of its motion and its velocity
Units: Joules πΎπΈ =1
2ππ£2
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Example
Calculate the gravitational potential energy a 2500 kg roller coaster has at the top of a 9 meter hill.
Calculate the kinetic energy a 0.050 kg bullet has when traveling 380 m/s.
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Example
The gravitational potential energy, with respect to Earth, that is possessed by an object is dependent on the objectβs
a) acceleration
b) momentum
c) position
d) speed
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Example
As a ball falls freely toward the ground, its potential energy
a) decreases
b) increases
c) remains the same
Justification???
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Example
As a ball falls freely toward the ground, its kinetic energy
a) decreases
b) increases
c) remains the same
Justification???
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Springs
Hookeβs law
k = spring constant (in N/m) ; this is a measure of how βstiffβ or βslinkyβ the spring is
x = the distance the spring is stretched or compressed
πΉ = ππ₯
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Springs
Elastic potential energy is the stored energy in a stretched or compressed spring
Example: energy stored in spring loaded nerf gun
Units: Joules
ππΈ =1
2ππ₯2
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Example
A 2.0 kg mass is placed on the end of a spring and the spring stretches a distance of 0.8 meters.
What is the spring constant of the spring?
If the same spring were stretched to 1.5 meters, how much energy would be stored in the spring?