do work!
DESCRIPTION
Our Midterm Review ProjectTRANSCRIPT
![Page 1: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/1.jpg)
Corinne Goldstein,Ali Lubin,
Bridget Miller,and
Stephen Desiletspresent…
![Page 2: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/2.jpg)
In association with DreamWORKS studios…
![Page 3: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/3.jpg)
A Chapter 6 Production…
![Page 4: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/4.jpg)
![Page 5: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/5.jpg)
…And Energy
![Page 6: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/6.jpg)
What’s this all about?
![Page 7: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/7.jpg)
Well, let’s look at the terms…
![Page 8: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/8.jpg)
Work – Measured in Joules
Energy – Also measured in Joules
Spring Constant – Measured in Newton/meters
Power – Measure in Watts
![Page 9: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/9.jpg)
Well Work and Energy are both measured in
Joules.
Are they the same thing?
![Page 10: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/10.jpg)
NO
![Page 11: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/11.jpg)
Work (W)
• Work is the Transfer of Energy, or more simply put, Force exerted over a Distance
• W = FdcosӨ– F = Magnitude of Force (Newtons)– d = Magnitude of Displacement– Ө = Angle between Force and Displacement
![Page 12: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/12.jpg)
So 1 Joule = 1 Newton x 1 Meter
![Page 13: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/13.jpg)
And if someone walks down a horizontal road…
Work is done by that person…
But the work done by gravitational force is zero since the
displacement is perpendicular to the direction of the force
![Page 14: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/14.jpg)
HOWEVER…
![Page 15: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/15.jpg)
Energy of a body is its Capacity to do
Work
![Page 16: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/16.jpg)
EnergyThere’s 3 Types!
![Page 17: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/17.jpg)
Kinetic Energy (KE or K)
• The Energy of Motion
• KE = ½ mv²– m = mass of the object
– v = velocity of the object
![Page 18: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/18.jpg)
Gravitational Potential Energy
• The stored energy an object has due to its position above earth’s surface
• PE = mgh– m = mass of the object– g = acceleration of gravity– h = height of the object relative to earth (or
some other zero level)
![Page 19: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/19.jpg)
Elastic Potential Energy (PEs)
• Energy a Spring has by virtue of being stretched or compressed
• PEs = ½ kx²– k = Spring Constant – Measures the strength
of the spring in N/m– x = Distance the spring is stretched or
compressed
![Page 20: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/20.jpg)
Say, are Work and Energy related?
![Page 21: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/21.jpg)
YES
![Page 22: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/22.jpg)
Work exerted on an object is equal to the difference between
an object’s initial and final Energies.
![Page 23: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/23.jpg)
So…
![Page 24: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/24.jpg)
WKE = KE – KE0 = mv² - ½ mv0²
Wgravity = PE – PE0 = mgh – mgh0
ormg(h-h0)
WPEs = PEs – PEs0 = ½ kx² - ½ kx0²
![Page 25: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/25.jpg)
One of those equations even has its own
theorem!
![Page 26: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/26.jpg)
Can you guess which one?
![Page 27: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/27.jpg)
Work-Energy TheoremWKE = KE – KE0 = mv² - ½ mv0²
Or in English terms…
The work done by an object by an outside force is equal to the difference between the
object’s final and initial kinetic energies
![Page 28: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/28.jpg)
So have I mastered the Force?
![Page 29: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/29.jpg)
Not yet.Much to learn there still is,
Young Padawan.
![Page 30: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/30.jpg)
Like the difference between Conservative Forces and Nonconservative Forces
![Page 31: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/31.jpg)
Conservative Forces
• Force that exerts the same amount of force on an object moving between two points, no matter what path the object takes
• Types:– Gravitational Potential Energy– Elastic Spring Force– Electric Force
![Page 32: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/32.jpg)
What’s all that Mumbo Jumbo mean, though?
![Page 33: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/33.jpg)
Let’s think about it.
![Page 34: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/34.jpg)
Take the Wgravity for example…
The equation is Wgravity = mg(h-h0)
So if an object falls 50 meters, the work exerted on the object by gravity won’t change whether the object fall straight
down or falls on an angle. All that matters is the initial and final heights.
![Page 35: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/35.jpg)
Well then what’s a Non-Conservative Force?
![Page 36: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/36.jpg)
Non-Conservative Force
• Force that exerts a different amount of work on an object moving between two points depending on what path the object takes
• Types:– Static and Kinetic Frictional Forces– Air Resistance– Tension– Normal Forces– Propulsion Force of a Rocket
![Page 37: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/37.jpg)
Okay, well what if I want to calculate the work due to non-
conservative forces acting on an object?
![Page 38: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/38.jpg)
Good Question!
![Page 39: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/39.jpg)
Effectively, you can calculate the work exerted on an object by
non-conservative forces by…
finding the difference between the initial and final energies due to
conservative forces acting on an object.
The difference is the work due to non-conservative forces that acts on
the object
![Page 40: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/40.jpg)
So…
Wnc = ΔKE + ΔPE + Δ PEs
orWnc = ( ½mv² - ½ mv0²) + (mgh – mgh0) + (½ kx² - ½kx0²)
(Δ means change)
![Page 41: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/41.jpg)
Let’s Conserve Energy!
![Page 42: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/42.jpg)
Mechanical Energy (ME or E) of and object is the sum of the
kinetic and potential energies of that object
E = KE + PE
![Page 43: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/43.jpg)
When the net work exerted on a moving object by non-
conservative forces is zero, the total mechanical energy of that
object remains constant…
![Page 44: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/44.jpg)
…In this case, KE and PE can be transformed into one another
as the object moves.
![Page 45: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/45.jpg)
Cool Beans!
![Page 46: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/46.jpg)
If there are no non-conservative forces acting on the object, then the initial and final total energies
should be equal
![Page 47: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/47.jpg)
So…
Wnc = (½mv² + mgh + ½kx²) - (½mv0² + mgh0 + ½kx0²)or
½mv² + mgh + ½kx² = ½mv0² + mgh0 + ½kx0²
![Page 48: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/48.jpg)
I GOT THE POWER!
![Page 49: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/49.jpg)
Power
• The Rate at which Work is done• P = W/t or• P = Fv
or • P = (FdcosӨ)/t
• Measured in Watts (W)
![Page 50: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/50.jpg)
So…
1 Watt = 1 Joule per second
![Page 51: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/51.jpg)
We’re Almost Done!
![Page 52: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/52.jpg)
Hey, remember howWork = Force x Distance?
![Page 53: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/53.jpg)
Well, if you plot Force on one axis of a graph and Distance on
the other, then you can calculate the Work exerted by finding the area under the line.
![Page 54: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/54.jpg)
Just likeArea = Length x Width,
Work = Force x Distance
![Page 55: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/55.jpg)
Time to Practice!
![Page 56: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/56.jpg)
Find the work exerted on a suitcase if the suitcase is being pulled with a force of 16.0 N at a 56.0º angle to the floor and the displacement of the suitcase is
63.0 cm.
![Page 57: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/57.jpg)
W = FdcosӨW = (16.0N)(0.63m)(cos56.0º)
![Page 58: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/58.jpg)
Degree Mode is your friend.
![Page 59: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/59.jpg)
W = 5.64 J
![Page 60: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/60.jpg)
An archer pulls a bowstring back a distance of 0.470m and then releases the arrow. The
bow and string act like a spring whose spring constant is 425
N/m. What is the elastic potential energy of the system?
![Page 61: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/61.jpg)
PE = ½kx²PE = ½(425N/m)(0.470m)²
PE = 46.9 J
![Page 62: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/62.jpg)
A motorcyclist is trying to leap across a canyon by driving
horizontally off the cliff at a speed of 38.0 m/s. Ignoring air
resistance, find the speed at which the motorcycle strikes the ground on the other side. The motorcycle starts at a height of 70.0m and will
end at a height of 35.0m.
![Page 63: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/63.jpg)
½ mv² + mgh = ½mv0² + mgh0
(mass cancels out)
½v² + (9.8m/s²)(35.0m) = ½(38.0m/s)² + (9.8m/s²)(70.0m)
V = 46.2 m/s
![Page 64: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/64.jpg)
A 0.20kg rocket is launched from rest. It takes a roundabout route until it reaches a height of 29m above its
starting point. In the process, 425J of work is done on the rocket by non-conservative forces (the burning
propellant). Ignoring air resistance and the mass lost due to the burning of the fuel, find the speed of the rocket when
it is 29 m above its starting point.
![Page 65: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/65.jpg)
Wnc = ½mv² + mgh – (½mv0² + mgh0) 425J = [½(0.20kg)v² + (0.20kg)(9.8m/s²)(27m)] – [½(0.20kg)(0m/s)² + (0.20kg)(9.8m/s²)(0m)]
V = 61 m/s
![Page 66: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/66.jpg)
A car starts from rest and accelerates in a positive
direction. The car has a mass of 1.10 x 10³kg and accelerates
at +4.60m/s² for 5.00s. Determine the average power
generated by the force that moves the car.
![Page 67: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/67.jpg)
V = v0 + atv = 0m/s + (4.6m/s)(5.00s)
v = 23 m/s
P = FvP = mav
P = (1.10 x 10³kg)(4.6m/s²)(23m/s)P = 1.16 x 10^5 W
![Page 68: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/68.jpg)
Th-Th-That’s All Folks!
![Page 69: Do Work!](https://reader035.vdocument.in/reader035/viewer/2022062319/555cfc88d8b42a08668b5123/html5/thumbnails/69.jpg)
It’s Physics-tastic!