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A force that causes a Displacement of an object does
Work on that object.
Work is the product of theMagnitudes of the componentOf a force along the direction
And the displacement.
W = Fd
Work has the dimensions of Force times length.
Thus the units areN * m
Or the Joule (J)
Work is only done when Components of a force are Parallel to a displacement.
W = Fd (cos θ)
A tugboat pulls a ship with a forceOf 5.00 X 103 N. How much workIs done by the tugboat on the
Ship if it moves 3.00 km?
1.50 X 107 J
How much work is done on a Vacuum cleaner pulled 3.0 m by
A force of 50 N at an angle of30.0° above the horizontal?
130 J
Energy isThe capacity to Do work or to Produce heat.
Kinetic energy is the energy Of motion
KE = ½mv2
The formula for kinetic energyWill be used often…
A 7 kg bowling ball moves at 3 m/s.How much kinetic energy does my
Ball have? How fast must a Ping-pong ball (4.5) move to haveThe Same kinetic energy as the
Other ball?
31.5 J 160 m/s
Calculate the KE of an 8.0 X 104 kg airliner Flying at 600 km/h.
1.1 X 109 J
The work-kinetic energy theoremSays that the net work done onAn object is equal to the change
In the kinetic energy of The object.
The turns into a formula…
W = ΔKE
A 105 g hockey puck is sliding Across the ice. A player exerts a
Constant 4.5 N force over a Distance of 0.15 m. How much Work is does the player do on The puck? What is the change
In the puck’s energy?
0.68 J
Power is the rate at whichEnergy is transferred.
Or better stated as…
P = WΔt
or P = Fv
The SI unit for power is the Watt.
A watt is defined as 1 J/s.
Horsepower can also be used, And is equal to 746 W.
A 193 kg curtain needs to be raised7.5m in as close to 5 s as possible.Three motors are available. The Power rating on each motor is
1 kW, 3.5 kW and 5.5 kW. WhichMotor is best for the job.
The 3.5 kW motor is best.
A 1000 kg elevator carries a Max load of 800 kg. A constant
Frictional force of 4000N retardsThe motion. What minimum powerMust the motor deliver to lift the
Fully loaded elevator at a Constant speed of 3 m/s ?
66 kW
There are 6 different types of Simple machines.
A lever and FulcrumAn inclined planeWheel and axle
WedgePulleyScrew
Wheel & Axle
Inclined Plane
ScrewWedge
LeverPulley
The point of a machine is to Make work easier.
The amount that the work Gets easy is called
Mechanical Advantage.
MA = Output ForceInput Force
Fout
Fin
=
IMA = de
dr
IMA is the Ideal Mechanical Advantage
de = distanceexerted
dr = distance Of the object
Efficiency is a measure of How well a machine works.
eff = Wout
Win
A gasoline car is only about 30% efficient, where as an electric
Car is about 90% efficient!!
eff =MAIMA
A bike wheel has a radius of 35.6 cm and a gear with radius of
4 cm. When the chain is pulled 155NThe rim moves 14 cm. the efficiency
Is 95%. What is the IMA? WhatIs the MA? What is the resistance
Force? How far was the chain pulled?
0.112 0.106 16.4 1.57
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