king fahd university of petroleum & minerals
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King Fahd University of Petroleum & Minerals. Mechanical Engineering Dynamics ME 201 BY Dr. Meyassar N. Al-Haddad Lecture # 36. Chapter 18 Planar Kinetics of Rigid Bodies: Work and Energy. Kinetic Energy. General. Translation. Rotation. Rotation. - PowerPoint PPT PresentationTRANSCRIPT
King Fahd University of Petroleum & Minerals
Mechanical EngineeringDynamics ME 201
BYDr. Meyassar N. Al-Haddad
Lecture # 36
Chapter 18Planar Kinetics of Rigid Bodies:
Work and Energy
Kinetic Energy
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Example
K.E. of the Body of Bike and man ( translational )
2)(2
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K.E of the wheel ( Translational + Rotational )
22
2
1
2
1 Owheel ImT
Total K.E. = 2 Twheel +T B+Man
Total K.E? .
Example 18-1 mB=6 kgmD=10 kgmC=12 kgNo slippingTotal K.E = ?
Block (Translation)
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2
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Disk (Rotation)222 )
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sradrD
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1.0
8.0
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ProblemwAB=wCD=10 IbwBC=20 IbTotal K.E = ?
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The work of a force
forcevariableaofWork
dsθFUsF cos
forceconstantaofWork
sθFU ccF )cos(
::
::ntdisplacemevertical:
weightaofWork
W
W
U
Uy
yWUW
• Work of a Spring Force
)2
1
2
1( 2
12
2 ksksU s
12 sswhere
Force Perpendicular to the displacement-Weight-Normal reaction
Force That Do No Work
Rolling resistance force Fr
Fr acts at point which has zero velocityThe point is not displaced
Pin Reaction
Ot
On
Oy
Ox
Pin Reaction Do No workAct on zero velocity and create no displacement
The Work of a couple
-Do work only when the body undergoes a rotation
-Translation : positive work cancels the negative work
-Rotation
θdM
θdrFθdr
Fθdr
FdUM
)(
22
)( 122
1θθMdθMU
θ
θM
dθr
Sd θ 2
m =10 kg M = 50 NmP = 80N, unstretched 0.5 m
total work? 90~0θ
J2.147)5.1)(81.9(10
Example 18-2
)(2
1)
2
1
2
1( 2
12
22
12
2 sskksksU s ms
ms
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25.05.075.0
2
1
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)( 12 θθMUM
)( ygmUW