Download kinetic energy

‫الفيزياء العامة مقرر ‪110‬‬
‫السنة التحضيرية للعام الجامعي‬
‫‪1433‬هـ ‪1434 -‬هـ‬
‫تنفيذ‬
‫الدكتورة‪/‬سميرة القحطاني‬
‫استاذ مساعد‬
‫‪[email protected]‬‬
Phys 110
Fundamentals of Physics
8th Edition
HALLIDAY * RESNICK
Ch-7
Kinetic Energy and Work
‫الطاقة الحركية والشغل‬
‫في هذا الفصل سوف نركز على دراسة‬
only one way in
which energy can
be transferred
(Work)
only one type
of energy
Kinetic energy
Nature of Energy
You use energy 
when you:
hit a softball. 
lift your book bag. 
compress a spring. 
Living organisms need energy for
growth and movement.
Energy is involved when: 
a bird flies. 
a bomb explodes. 
rain falls from the sky. 
electricity flows in a wire. 
Properties of Energy
- Energy is measured
Energy can be transformed from one
type to another
in the same units as
work
.If the energy transformed and transferred
we find that the total amount is always the
same (energy is conserved ).
- Energy is a scalar quantity
Radiant Energy
Thermal Energy
Electrical
Energy
Chemical Energy
Mechanical Energy
Nuclear Energy
Magnetic Energy
Kinetic Energy is the energy of motion.
Potential Energy is stored energy.
Potential energy + Kinetic energy = Mechanical energy
Kinetic energy is energy associated with the state of
motion of an object
The faster the object moves , the greater is its
kinetic energy .
When the object is stationary , its kinetic energy is
zero .
K ( kinetic energy ) is Scalar quantity .
v  v 0  2a (x  x 0 )
2
2
v 2  0  2 (0.26 m / s 2 ) (3.2 x103 m)
v  40.8 m / s
1.2 x 10 6 N
5
m

1
.
22
x
10
kg
2
9.8 m /s
K  2 ( 12 mv 2 )  (1.22 x 105 kg) (40.8 m / s) 2
 2.0 x 108 J
‫في هذا الفصل سوف نركز على دراسة‬
only one way in
which energy can
be transferred
(Work)
only one type
of energy
Kinetic energy
Where
is the angel
between the direction of the
displacement
and the
force
F = 5 i - 2 j + 2k
d=2i -3j - k
W= +10 +6 2
Properties of Work
Energy transferred to
the object
Work is a scalar
quanti
ty
Positive work
+W
1 J  kg  m / s  1 N  m
2
2
Unite Joule
Energy transferred
from the object
negative work
-W
Work and Kinetic Energy
Work done by an External Force
Work – kinetic energy theorem
 K  K f  Ki  W
 change in the kinetic

 energy of a particle
  net work done on 
  

the particle
 

Kf  Ki  W
 kinetic energy after   kinetic energy   the net 

  
  

 the net work is done   before the net work   work done 
16
‫انواع الشغل‬
The force dose positive
work on the object
When it has a vector
component in the same
direction as the displacement
The force dose zero on
the object
When it has vector
component
perpendicular as the
displacement
The force dose
negative work on
the object
When it has a vector
component in the
opposite direction as
the displacement
‫امثلة لتوضيح نوع الشغل‬
‫‪A‬‬
‫‪B‬‬
‫القوة نفس اتجاة االزاحة‬
‫القوة عكس اتجاة االزاحة‬
‫‪F‬‬
‫‪d‬‬
‫‪C‬‬
‫القوة عمودية على اتجاة االزاحة‬
‫‪Ø=0‬‬
‫)‪a‬‬
‫‪1‬‬
‫‪mV 2‬‬
‫‪2‬‬
‫‪V 2‬‬
‫‪k ‬‬
‫‪1‬‬
‫‪‬‬
‫‪mV 2‬‬
‫‪2‬‬
‫‪1‬‬
‫‪‬‬
‫‪m ( 2) 2‬‬
‫‪2‬‬
‫‪ 2m‬‬
‫‪Kf‬‬
‫‪Kf‬‬
‫‪Kf‬‬
‫‪1‬‬
‫‪k ‬‬
‫‪mV 2‬‬
‫‪2‬‬
‫‪V  3‬‬
‫‪1‬‬
‫‪mV02‬‬
‫‪2‬‬
‫‪1‬‬
‫‪Ki ‬‬
‫‪m( 3) 2‬‬
‫‪2‬‬
‫‪K i  4.5m‬‬
‫‪Ki ‬‬
‫‪W  2  4.5‬‬
‫‪Ki  K f‬‬
‫‪ 2.5‬‬
‫الشغل يكون سالب النها بدات من ‪ 4.5‬وانتهت الى ‪ 2‬اذن الطاقة الحركية قلت‬
b) k  1 mV 2
2
V  2
1
Ki 
mV 2
2
1
Ki 
m( 2) 2
2
K i  2m
Ki  K f
1
k 
mV 2
2
V  2
K
f
K
f
K
f
1

mV 2
2
1

m ( 2) 2
2
 2m
‫‪ Ki‬‬
‫الشغل هنا سالب‬
‫‪f‬‬
‫‪W  K‬‬
‫‪ 2  4.5‬‬
‫‪  2 .5‬‬
‫‪W  K f  Ki‬‬
‫‪ 22‬‬
‫الشغل هنا صفر‬
‫‪0‬‬
‫)‪c‬‬
Methods for calculating work
work done by Fnet
work done by f1 +
work done by f2
FN
FN
F1=20N
F1=20N
F2=10N
30
40
Fg
F2=10N
Fg
FN
FN
F1=20N
F1=20N
F2=10N
30
40
Fg
F2=10N
Fg
a)

Work done by F1
:
W1  F1 d cos 1  (12.0 N)(8.50 m)(cos 30 )
 88.33 J
Work done by F2 :
W2  F2 d cos  2  (10.0 N)(8.50 m)(cos 40 )
 65.11 J
Total work done
:
W  W1  W2  88.33 J  65.11 J
 153.4 J  153 J
During the displacement, what is the work Wg

done on the safe by the gravitational force F
and what is the
work WN done on the safe by the

normal force N from the floor?
(b)
g
Wg  mgd cos 90  0

WN  Nd cos 90

0
(c)
The safe is initially stationary. What is its
speed vf at the end of the 8.50 m
displacement?
Work done on object equals increase in kinetic energy :
W  K f  K i  mv f  mv i
1
2
2
1
2
2
2W
2 (153.4 J)
vf 

m
225 kg
 1.17 m / s
We have assumed no frictional forces exist.
(a)
How much work does this force from the
wind do on the crate during the
displacement?
Work done by the wind force on crate :
 
W  F  d  (2.0 N ) iˆ  (  6.0 N ) ˆj   ( 3.0 m) i 


 (2.0 N ) ( 3.0 m) iˆ  iˆ  (  6.0 N ) (  3.0 m) ˆj  iˆ
 (  6.0 J ) (1)  0   6.0 J
The wind force does negative work, i.e. kinetic energy is
taken out of the crate.
(b) If the crate has a kinetic energy of 10 J

at the beginning of displacement d , what is

its kinetic energy at the end of d ?
W  K f  Ki
 6 j  K f  10 j
 6 j  10 j  K f
Kf  4j
‫امثلة وتطبيقات‬
‫‪5kg‬‬
‫‪Q.1‬‬
Q.2
Q.3
Q.4
Q.5
Q.6
Q.7
Q.8
‫مالحظاااااااااات هااااااااااااااااااااااااااااااامة‬
‫بعض المصطلحات الموجودة في ‪Ch7‬‬
‫المصطلح العلمي (انجليزى)‬
‫المصطلح العلمي(العربي)‬
‫‪Kinetic Energy and Work‬‬
‫الطاقة الحركية والشغل‬
‫‪Energ‬‬
‫الطاقة‬
‫‪energy is conserved‬‬
‫حفظ الطاقة‬
‫‪principle‬‬
‫مبدا‬
‫‪Kinetic energy‬‬
‫الطاقة الحركية‬
‫‪Work‬‬
‫الشعل‬
‫‪transferred‬‬
‫تحويل او نقل‬