Mudah dan Aktif Belajar Fisika untuk Kelas XI
76
Gambar 3.13
a Keadaan awal benda dalam posisi seimbang.
b Pegas ditarik sejauh simpangan y
2
. c Posisi benda kembali ke titik
setimbang karena gaya
pegas F = –ky
2
.
5A11;18 55A79 ?C5B91 H17 49=99;9 ?58 = 19A H17 25A141 141
;5C97791=:9;1=1BB1:59B19A
;7= 415A351C17A1E9C1B949C5=1C
C5AB52DC
=B 8
9AC5A:DC5AB52DC=5=99;9=1BB1 ;7=
= N
;7 5A79?C5B91H1749=99;919AC5A:D14118
N ;7
=B =N
14955A79?C5B91H1749=99;919AC5A:D14118N :?D5
b. Energi Potensial Elastis Pegas
5A79 ?C5B91 51BC9B 571B 25A2541 4571 55A79 ?C5B91 141 D=D=H1
5A79?C5B91571B1411855A79H1749=99;9571B1;921C
141H15AD21811:171C1DA57171571B
1H1H1725;5A:1141 571B =5=D7;9;1 571B DCD; =5A5717
5A81C9;13
1413
=D1 =D1571B411= ;51411 B5C9=217
5A79 ?C5B91 571B 41 55A79 ;95C9;H1 ?
141 3
413
571B=5=99;9B9=171B5:1D8
2 41
2 1:17 2
2 58 ;1A51 141 C1A9;1 B525B1A 2 41
571B =51A9; ;5=219 2541 B5BD19 D;D= 5FC?
571B
K 5B1AH1DB181H17491;D;1571B41A9;51411
2 ;5
2 2B1=1
25B1A45715AD218155A79?C5B91571B1C1A1 2
41 2
2
571B
4
, 25B1A5A94181?B9B92541
2 2
2
2
2
2 2
2 571 45=9;91 25B1AH1 DB181 H17 491;D;1 ?58 71H1 571B
49H1C1;1 4571 5AB1=11
571B 571B
4571
571B
2 K
5C9;1 571B 4951B;1 571B 1;1 =51;D;1 75A1; 81A=?9; ,51=1 5A75A1;1H1 571B =5711=9 5AD2181 55A79 ;95C9;
=5:149 55A79 ?C5B91 571B 1C1D B5219;H1
-941; B51=1H1 571B =51;D;1 75A1; 81A=?9; 571AD8 71H1 D1A 1;1 =5=2D1C 571B
25A85C9 141 ?B9B9 ;5B5C9=2171
1 2
3
y
2
y
2
y
1
=0
Contoh
3.8
1 5AD218155A79?C5B91
p
E
K ;7
=B
=K=K 1495AD218155A79?C5B91B525B1A:?D5
2 .B181H17491;D;171H125A1C
K K
K;7
=B =K=
.B181?B9C96;1A511A1871H125A1CB51A1845711A185A94181 149DB181H17491;D;171H125A1CB525B1A:?D5
Sumber: Fisika untuk Sains dan Teknik, 1998
Tantangan
untuk Anda
Perhatikan gambar di atas. Jika seorang ahli gizi menyatakan
bahwa pada pizza isi daging dan keju tersebut mengandung energi
16 megajoule, bagaimana pendapat Anda jika dikaitkan
dengan konsep Fisika? Bagaimana cara mendapatkan angka tersebut?
Usaha, Energi, dan Daya
77
Tes Kompetensi Subbab
B
3,-0..6-6.5+0 ,52D1821CD;53925A=1BB174951B;141A9;1C15
B58977125B1A55A79;95C9;H1749=99;9H114118 :?D5
9CD7;51:D121CDC5AB52DC
?29 25A=1BB1
;7 B5417 25A75A1; 4571 ;5351C1;=:1=C921 C92149A5=4125A85C9
B5C518=55=D8:1A1;=
-5CD;118 1
71H1A5=141=?2941 2
DB181H17495A?5841A9575A5=1 5A5C1 =191 H17 =1BB1H1 ;7 4951B;1 41A9
D31;29417=9A979394571BD4DC;5=9A971 JC5A81418?A9I?C1
9;11:179C1B129417
=9A97
=41 =B
C5CD;15AD218155A79 ?C5B914941;5A5C1B5C518=55=D8:1A1;
=
54125A=1BB1;74951B;141A9;5C97791
3= 1
9CD718DB181H17491;D;171H17A1E9C1B9 1412541C5AB52DC
2 9CD71825A;DA17H155A79?C5B917A1E9C1B9
2541C5AB52DC 54125A=1BB1
;7:1CD8=5775939A41A91C1B
29417=9A974571BD4DC;5=9A971J
541 C5AB52DC=5D=2D;B52D18571BH17C5A5C1;
=
41A95C1;B5=D1
9;1 =41571B
C5AC5;1=1;B9=D=B5:1D8
3=89CD7;?569B95 75B5;1C1A121?;457129417=9A97
Kata Kunci
• energi kinetik • energi potensial
571B25AC1=2181:17
3=;5C9;14925A971H1
5A11;1855A79?C5B91 571B:9;171H1141571BC5AB52DC49:149;1;1991C
8 9;5C18D9
1 3=
=
1 F
=
= 9;1
1
F =
== 1
== 14925B1A55A79?C5B9151BC9B571B14118
Contoh
3.9
C. Gaya Konservatif dan Hukum Kekekalan Energi Mekanik
5A81C9;1 3
,52D18 571B 495C1;;1 49 1C1B 1C19 41 B118 B1CD D:D7H1 499;1C;1 141 49497
5=D491 B52D18 21?;
25A=1BB1 =5D3DA4571;5351C1C51C;51A18571B
9;11C19
41C1A41939B5AC1571BH19451B9BC5=1;1=5=5D89D;D=??;5 K
9 4571 14118 71H1 141 571B B11C D:D7 2521BH1 25A75B5A B5:1D8
51411 H17 49979;1 141 B9BC5= C5AB52DC 14118 55A79
;95C9;C5ADB1C141=1BB121?;B58977155A79;95C9;571B491219;1 ;921CH1 =1BB1 571B 491771 B171C ;539 41A9141 =1BB1 21?;
5C9;121?;=5H5CD8571B1:D21?;25A;DA17B1=191;89AH1 25A85C9 ;1A51 71H1 571B H17 =51F1 71H1 4?A?71 41A9 21?;
5A81C9;13
5=D4911A1821?;25A219;1;921C71H1 571B 25;5A:1
;921CH1 21?; =5=5A?58 55A79 ;95C9;H1 ;5=219
B55AC9 B11C 21?; =5H5CD8 571B F11DD 1A18H1 25A2541
1?;
Gambar 3.14
Gaya pada pegas merupakan gaya konservatif.
m m
m x
v
v
k
2
3 1
licin
x
1
x
2
x = x
2
– x
1
licin
licin
Mudah dan Aktif Belajar Fisika untuk Kelas XI
78
Tugas Anda 3.2
Sebutkan contoh-contoh gaya konservatif yang ada di sekitar Anda.
Gambar 3.15
Seseorang sedang melakukan usaha memindahkan peti.
;589171 55A79 ;95C9;H1 141 B118 B1CD 1A18 75A1;H1 C5C19 =5=5A?58 55A79 ;95C9;H1 ;5=219 141 1A18 75A1; H17 19 H19CD
;5C9;1 21?; 25A219; ;5 ?B9B9 B5=D1 3 141 5A9BC9F1 C5AB52DC DB181 H17 491;D;1 71H1 571B
9
C941;=57D21855A79=5;19;B9BC5=571B
1H1H17491;D;1?58 571BC5AB52DC25AB961C;?B5AE1C96
1H17A1E9C1B9:D7125AB961C;?B5AE1C96
411C;1841=5:51B;1=571171H17A1E9C1B925AB961C;?B5AE1C96 1A9BD4DC1417H171971H1;?B5AE1C96:D71=5=99;939A9218F1
:D=18DB181H17491;D;171H11411AC9;52541491771B521719 1AC9;514118?
141;51411B5C9=217?B9B9
171H1571B 141 3?C?8 C5AB52DC 49H1C1;1 4571 5AB1=11
9 K
-18D;18 41 DB181 H17 491;D;1 ?58 71H1 571B C5AB52DC 5A81C9;1 ;5=219 3
;5C9;1 2541 25A9418 41A9 ?B9B9
H17=5=99;9B9=171 1
;5?B9B94571B9=171 1
25B1ADB181 H17491;D;171H1571BC5A8141254149H1C1;145715AB1=11
K 1
K 1 1
-141 571C96 =5H1C1;1 218F1 1A18 71H1 571B 25A1F11
4571 1A18 5A94181 1 . , G - + +
+-+-+,1 41
1 571 45=9;91 5AB1=11 411C 49H1C1;1 4571
K 1 1
K 1
1 1
1 1
1 1
1 1
1 5A41B1A;1 5AB1=11 :51B18 218F1 DB181 H17 491;D;1
?58571BC941;=57D21855A79=5;19;B9BC5=41C941;25A71CD7 141?B9B91F141?B9B91;89A2541H1749;51971H1571BC5AB52DC
5A81C9;13
,52D185C9499418;1;5C5=1C19 B5C9779
.B181 H17 495AD;1 DCD; =5=9418;1 5C9 14118 K
-141571C96C9=2D;1A511A1871H125A1C25A1F11 4571 1A18 75A1; 5C9
.B181 ;5C9;1 =5=9418;1 5C9 C941; 25A71CD7 141 1:17 9C1B1H17491D95C9C5C1925A71CD714125B1A5AD2181C9779
5C941A9;54D4D;11;89A;5;54D4D;11F1H1
9;15C9499418;1 179;5?B9B91F1H1DB181H17491;D;1H114118
,531A1 =1C5=1C9B DB181 C?C1 H17 491;D;1 DCD; =5=9418;1 5C9 41A9
21F18 ;5 1C1B 1D 499418;1 179 ;5 21F18
14118
C?C
K 5B1A DB181 5=94181 B52D18 5C9 41A9 ;54D4D;1 1F1 89771
;5=219 ;5 ;54D4D;1 1;89AH1 25A919 ?
149 411C 49B9=D;1 218F1 DB181 H17 491;D;1 ?58 71H1 ;?B5AE1C96 1;1 25A919 ?
:9;1 ;54D4D;1 1;89A 2541 ;5=219 ;5 ;54D4D;1 1F1H1
