8/17/2019 Force 2.10-2.12 Student Copy
1/15
2.10 – 2.11
8/17/2019 Force 2.10-2.12 Student Copy
2/15
Form 4© COPYRIGHT BY SUPER EDUCATION GROUP (JO
2.10 – 2.11
PREPARED BY JJ R!EON P"#$ 1© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
8/17/2019 Force 2.10-2.12 Student Copy
3/15
F
% %
F&'
F
'
2.10 – 2.11
2.10,2.11 UNDERSTANDING WORK, ENERGY AND EFFICIENCY
A Wor
1. Work is the product of applied force and !"#$%&'ement in the direction of the applied force.
2. When the work is done ener(y is transferred from one object to another.
3. The work done is equal to the amount of ener(y transferred.
4. The SI unit for work is )o*%e.
The formulae of work
WORK = FORCE X DISPLACEMENT
W = F ! s
No wor "# !one w+en
1- The object is stationary
2) The direction of motion of the object is perpendicular to that of the applied force
PREPARED BY JJ R!EON P"#$ 2© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
W : work in Joule/J
F : force in Newton/N
s : displacement in
Work done
Force and displacement in the samedirection
Force and displacement in different directions
W = F.s W = Work F = Force s = displacement
W = F X sW = F s cos θ W = work F = force s = displacement θ = angle between force
and displacement
F
F Y F Y
F
F&
8/17/2019 Force 2.10-2.12 Student Copy
4/15
D%*"+$m$,- / m
2.10 – 2.11
Diagram (a) Diagram (b)
Diagrams (a) and (b) shows a boy pshing a load and a weightlifter lifting aload of !" kg
a) #alclate the work done
i. by the boy
W = F.s = 20 x 2 = 40 Nm or 40
ii. by the weightlifter
W = F.s = m!h
= "0 x #0 x 2 = #200 Nm or #200
$. %&man is plling a bo' with a force of " at an angle of !"o from the hori&ontal.#alclate the work done to mo*e the bo' to a distance of + m.
Wor$ = %omponent of force x displacement&'n the direction of displacement)
= (0 cos "0o x = 2( x = *(
PREPARED BY JJ R!EON P"#$ /© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
8/17/2019 Force 2.10-2.12 Student Copy
5/15
2.10 – 2.11
"!ample 1
"!ample 2
#$ %
&$$
s ' ( m
"!ample 3
"!ample 4
) ' &$$ %
S ' $.# m
PREPARED BY JJ R!EON P"#$ 4© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
For+$ F
s
8/17/2019 Force 2.10-2.12 Student Copy
6/15
2.10 – 2.11
PREPARED BY JJ R!EON P"#$ © COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
8/17/2019 Force 2.10-2.12 Student Copy
7/15
%
For+$ F
2.10 – 2.11
Ener(y
1. "ner*+ is the potential to do work.
2. "ner*+ cannot be created nor be destro+ed.
3. "!ist in ,arious forms such as $otent"&% ener(y, "net"' ener(y- electrical ener*+- sound ener*+-
nuclear ener*+- heat and chemical ener*+
"ner*+ is !e"ne! as the capacit+ to do work.
Wor "# !one when ener(y "# 'on/erte! from one form to another.
The unit of work is Nm or o*%e-
A.Wor !one &n! t+e '+&n(e "n "net"' ener(y
1. inetic ener*+ is ener*+ of an object due to its motion.
2. /efer to the fi*ure abo,e-
3. "!ample 0 small car of mass 1$$ k* is mo,in* alon* a flat road. The
resultant force on the car is 2$$ %.
a What is its kinetic ener*+ of the car after mo,in* throu*h 1$ m b What is its ,elocit+ after mo,in* throu*h 1$ m
Solution : Given : m = 100 k ! F = "00 N
a. #inetic ener$! %k = Fs
= "00 & 10= "000 J
'. (elocit$! v ) * mv " = "000
v = +.," m s
-1
PREPARED BY JJ R!EON P"#$ © COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
Work ' )s
' mas
' m ,2
The formulae of inetic ener*+- "k ' m,2
Through, v 2 = u2 +2as
u = 0
and, as = ½ v 2
8/17/2019 Force 2.10-2.12 Student Copy
8/15
2.10 – 2.11
. Wor !one &n! (r&/"t&t"on&% $otent"&% ener(y
h ' 1.( m
1. 5ra,itational potential ener*+ is ener(y o &n o3)e't !*e to "t# $o#"t"on. $o##e##e! 3y &n o3)e't !*e
to "t# $o#"t"on "n & (r&/"t&t"on&% "e%!-
2. /efer to the fi*ure abo,e
W ' F s ' m( h
where- F 4 m(
So, Gr&/"t&t"on&% ener(y, E$ 4 m(+
PREPARED BY JJ R!EON P"#$ 3© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
8/17/2019 Force 2.10-2.12 Student Copy
9/15
2.10 – 2.11
PREPARED BY JJ R!EON P"#$ © COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
8/17/2019 Force 2.10-2.12 Student Copy
10/15
2.10 – 2.11
5r"n'"$%e o 'on#er/&t"on o ener(y
the principle of conser,ation of ener*+.
1. "ner*+ cannot be created or destro+ed but can be chan*ed from one form to another form.
2. E6&m$%e 6 a thrown ball upwards will achie,e a ma!imum hei*ht before chan*in* its direction and falls
3. "!ample in calculation 6 0 coconut falls from a tree from a hei*ht of 2$ m. What is the ,elocit+ of
coconut just before hittin* the earthGiven : = "0 m! u = 0 ! = . ms-" ! v =
% p = %k
m = * mv "
m2.32"03 = *mv "
v " = ,"! v = 1. m s-1
5ower
1. 7ower is the rate of doing or!"
rate of energ# transfor$ation"
4erefore! power! 5 =ti$eta!en
or!done
! so! 5 =t
W
Were! 5 : power in watt/W
W : work in 6oule/J
t : time to do work in seconds/s
2. 8nit6 9oule per second 9 s:1 or Watt W
3. 0 wei*htlifter lifts 1#$ k* of wei*hts from the floor to a hei*ht of 2 m abo,e his head in a time of $.# s.
What is the $ower (ener&te! b+ the wei*htlifter durin* this time
* ' ;.# ms:2
PREPARED BY JJ R!EON P"#$ 5© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
7a&imum 5otential ener$
#inetic ener$ decrease potential ener$ decrease
and potential ener$ and kinetic ener$
8ncrease increase
7a&imum
kinetic ener$
8/17/2019 Force 2.10-2.12 Student Copy
11/15
2.10 – 2.11
E"'"en'y
1.
8/17/2019 Force 2.10-2.12 Student Copy
12/15
2.10 – 2.11
,amy releases a $ kg metal ball from a bilding -" m high (ake acceleration
PREPARED BY JJ R!EON P"#$ 11© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
8/17/2019 Force 2.10-2.12 Student Copy
13/15
2.10 – 2.11 de to gra*ity as 1" ms/$)
a) %t the height of -" m0 the metal ball has (gra*itational potential energykinetic energy)
b) 2st before the metal ball hits the grond0 the ma'imm energy that it has is (gra*itationalpotential energykinetic energy).
c) #alclatei) he energy of the metal ball at the height of-" m.
3gra*itational = mgh
= ($) (1") (-")= 4"" 2
ii) the kinetic energy of the metal before it hits the grond.
+$inetic = +!ra,itational= -00
d) What is the principle sed in c ii)5
The principle of conser,ation of ener!y
. % motor lifting a weight 1 kg to a height of -." m in - s. he inpt energy spply to the motor in onesecond is $" 2. #alclate
a) power of the motor
o/er = /or$ donetime ta$en
= m!h t
= ) )&4.0) 4
= #0 /att
b) the efficiency of the motor
PREPARED BY JJ R!EON P"#$ 12© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
6etal ball
-" meter
8/17/2019 Force 2.10-2.12 Student Copy
14/15
2.10 – 2.11
+fficiency = seful ener!y output x #001 +ner!y input
= #0 x #00120
= (0 1
2.10 A55RECIATING T7E IM5ORTANCE OF MA8IMISING T7E EFFICIENCY OF DE9ICES
1. .
The unwanted ener*+ produced in the de,ice *oes to waste
inetic ener*+
"ner*+ loss due to "ner*+ loss "ner*+ loss "ner*+ loss due to friction at
friction in as heat as sound other parts in the
mo,in* parts en*ine
8/17/2019 Force 2.10-2.12 Student Copy
15/15
2.10 – 2.11
PREPARED BY JJ R!EON P"#$ 14© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)
Top Related