Dinamika Gerak smstr 1

Mata pelajaran : Fisika

Standar Kompetensi : Menerapkan Konsep dan Prinsip dasar kinematika dan dinamika benda

titik

Kompetensi Dasar : 2.2. Menerapkan hukum Newton sebagai prinsip dasar dinamika untuk

gerak lurus

Kelas/ Semester : X/ 1 (satu)

Alokasi Waktu : 10 Jam Pelajaran

BAB 3 DINAMIKA GERAK

RINGKASAN MATERI

Dinamika adalah: Ilmu yang mempelajari tentang gerak suatu benda dengan meninjau penyebab dari gerak

benda tersebut.

1. Hukum Newton

a. Hukum I Newton

Hukum I Newton menyatakan: Bila resultan gaya yang bekerja pada benda sama dengan nol atau

tidak ada gaya yang bekerja pada benda, maka benda yang diam akan tetap diam atau benda yang

bergerak lurus beraturan akan tetap bergerak lurus beraturan. Hukum I Newton mengungkapkan

tentang sifat benda yang cenderung mempertahankan kedudukanya atau dengan kata lain sifat

kemalasan bendauntuk mengubah kedudukanya. Sifat ini disebut Kelembaman/ Inersia. Hukum I

Newton disebut juga dengan hukum kelembaman.

Secara matematis Hukum I Newton dapat dituliskan:

............................. (3.1)

b. Hukum II Newton

Hukum II Newton menyatakan: ”percepatan yang dihasilkan oleh resultan gaya yang bekerja pada

suatu benda berbanding lurus dengan resultan resultan gaya yang bekerja pada benda tersebut dan

berbanding terbalik dengan massa benda itu”

Secara matematis Hukum II Newton dapat dituliskan:

atau ............................. (3.2)

Keterangan:

= resultan gaya (N)

m= massa benda (kg)

a = percepatan benda (m/s2)

c. Hukum III Newton

Hukum III Newton menyatakan: ” Jika benda pertama mengerjakan

gaya pada benda kedua, maka benda kedua akan mengerjakan gaya

pada benda pertama, yang besarnya sama tetapi arahnya

berlawanan. Hukum III Newton disebut juga hukum aksi-reaksi.

Hukum II Newton dapat dituliskan:

............................. (3.3)

LKS Fisika SMA Kelas X 1

Gambar 3.1: Mobil yang sidorong dan bergerak dengan percepatan a

a

FAksi

- FReaksi

Hukum tersebut dapat diartikan bahwa gaya hanya hadir sedikitnya ada dua benda yang saling

berinteraksi. Pada interaksi ini gaya-gaya selalu berpasangan.

Konsep gaya Aksi-reaksi Yaitu:

1. Gaya aksi-reaksi hadir jika dua benda berinteraksi

2. Gaya Aksi-reaksi bekerja pada dua benda yang berbeda

3. Gaya Aksi-reaksi besarnya sama, tetapi arahnya berlawanan

2. Beberapa Jenis Gaya/ Macam Gaya

a. Gaya Berat

Gaya berat yaitu: gaya yang bekerja pada suatu benda akibat benda tersebut berada dalam

pengaruh gravitasi bumi.

Secara matematis dapat dirumuskan:

............................. (3.4)

Keterangan:

W = berat benda ( N)

m = massa (kg)

g = Percepatan gravitasi (m/s2)

Contoh:

b. Gaya Normal

Gaya Normal yaitu: gaya yang dikerjakan oleh bidang pada benda apabila benda tersebut menekan

bidang, arah gaya normal selalu tegak lurus dengan permukaan bidang.

Contoh:

c. Gaya Tegangan Tali

Gaya tegangan tali adalah: gaya yang dikerjakan oleh tali terhadap sebuah benda yang diikat

dengan tali tersebut.

Contoh:

d. Gaya Gesekan


W

W

N

N

T

m

T

T

m

m

Gaya gesek yaitu: suatu gaya yang bekerja abtara dua permukaan yang bersentuhan dan bersifat

melawan kecenderungan gerak benda.

Contoh:

Secara matematis gaya gesek dapat dirumuskan:

............................. (3.5)

Keterangan:

Fges= gaya gesekan (N)

= Koefisien gesekan

N= gaya Normal (N)

3. Penerapan Hukum Newton

a. Benda pada bidang datar dan licin

............................. (3.6)

Keterangan:

F = Gaya (N)

m = Massa (kg)

a = percepatan benda (m/s2)

= Sudut antara gaya dengan perpindahan

b. Benda pada bidang datar yang kasar

c. Benda pada bidang datar yang licin dan ditarik oleh benda yang lain

Lihat massa m1

................(i)

Lihat massa m2

.............(ii)

Substitusi persamaan (i) ke (ii)


FfGesekan

F

m

Fx

m

F

α

FfGesekan

T

T

m2

m1

W1

a

Keterangan:

m1= Massa benda 1 (kg)

m2= Massa benda 2 (kg)

g = Percepatan Gravitasi (m/s2)

a = Percepatan benda (m/s2)

............................. (3.7)

d. Benda pada bidang miring yang licin

Gaya arah sumbu x

mamg sin

............................. (3.8)

Gaya arah sumbu y

(Resultan gaya arah sumbu y=0)

............................. (3.9)

e. Benda yang dihubungkan dengan tali melalui katrol

Jika m2>m1, maka

W2-W1= (m1+m2) . a

m2.g – m1.g = (m1+m2). a

(m2-m1).g = (m1+m2). a

............................. (3.10)

f. Benda yang digantung dengan tali

1. Benda diam

, a=0, karena benda diam

............................. (3.11)

2. Benda bergerak keatas dengan percepatan a

............................. (3.12)

3. Benda bergerak kebawah dengan percepatan a


mg

mg sin α

N

mg cos αα

α

m

m1

W1

T

W2

m2

T

a

T

m

W=mg

T

m

W=mg

a

T

m

W=mg

a

............................. (3.13)

g. Orang yang berada di dalam lift

1. Lift diam/ bergerak dengan kecepatan tetap

Maka nilai a=0

............................. (3.14)

2. Lift dipercepat ke atas dengan percepatan a

............................. (3.15)

3. Lift dipercepat ke bawah dengan percepatan a

............................. (3.16)

4. Lift diperlambat ke bawah

Maka nilai a= -a

............................. (3.17)

h. Benda yang digantung dengan dua utas tali pada keadaan setimbang.

............................. (3.18)


mg

N

mg

Na

mg

Na

mg

Na

W

T1T2

T3

KEGIATAN LABORATORIUM (TUGAS KELOMPOK)

A. Nama Kegiatan : Memahami Hukum Newton

B. Tujuan : Siswa Mampu menjelaskan dan menganalisis penerapan hukum I Newton,

II Newton dan III Newton tentang gerak

C. Alat dan Bahan

1. 2 buah uang logam.

2. 1 lembar kertas HVS.

3. 1 buah Ticker timer.

4. 1 buah Katrol kecil.

5. 1 buah beban (m) 1 kg

6. 3 buah beban (M) : 2,5 kg, 2 kg, dan 1,5 kg.

7. 1 rol kertas ticker timer dan kertas karbon.

8. 2 buah neraca pegas.

9. 1 buah statif

Kegiatan 1

Langkah kerja

1. Taruhlah 2 uang logam saling bertindihan diatas kertas HVS!

2. Tarik kertas dengan cepat pada posisi mendatar !

3. Ulangi kegiatan ini beberapa kali!

4. Berilah kesimpulan dari kegiatan ini!

Kegiatan 2

Langkah kerja

1. Rangkaian alat dan bahan seperti pada gambar di bawah ini!

2. Gunakan beban mulai yang massa terkecil sampai besar secara bergantian!

3. Amati pita ticker timer pada setiap beban (M).

4. Apakah kesimpulan dari kegiatan ini?

Kegiatan 3

Langkah kerja

1. Ikatkan sebuah pegas pada statif, sedangkan neraca pegas yang lain anda biarkan bebas lihat gambar di

bawah ini.


2. Perlahan-lahan, tariklah ujung neraca pegas yang bebas sampai pada skala tertentu. Catat skala yang

ditunjukkan oleh kedua neraca pegas. Ulangi tarikan Anda untuk skala-skala lain yang berbeda.

3. Apa kesimpulan dari kegiatan ini? TUGAS INDIVIDU

Jawablah pertanyaan dibawah ini dengan jelas dan benar

1. Sebuah benda bermassa m, padanya bekerja gaya F, hingga benda memperoleh percepatan a. Jika

massa benda dijadikan 2 m dan gayanya dijadikan 4F, maka percepatan benda menjadi ……

Jawab: ______________________________________________________________________________

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2. Berilah contoh gaya gesekan yang menguntungkan ….

Jawab: ______________________________________________________________________________

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3. Di dalam sebuah lift ditempatkan sebuah timbangan badan. Saat lift dalam keadaan diam

seseorang menimbang badannya, didapatkan bahwa berat orang tersebut 500 N. Jika lift bergerak ke

atas dengan percepatan tetap 5 m/s-2, g = 10 m/s-2, maka berat orang tersebut menjadi ……

Jawab: ______________________________________________________________________________

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4. Perhatikan sistem benda disamping!!! Gesekan tali dan katrol diabaikan (katrol licin), maka

percepatan sistem adalah ......... m/s²

Jawab: _________________________________________

_________________________________________


licin

m2= 2 kg

m1= 1 kg

5. Perhatikan sistem benda disamping!!! Gesekan tali dan katrol diabaikan (katrol licin), maka

tegangan tali sistem adalah ......... N

Jawab: _________________________________________

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Jawab: ___________________________________

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6. Berilah contoh-contoh gaya gesekan yang merugikan !

Jawab: ______________________________________________________________________________

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7. Sebuah mobil bermassa 800 kg pada suatu saat mesinnya menghasilkan gaya dorong 5400 N tetapi

hanya mendapat percepatan 6,5 m/s², maka besar gaya gesekkan yang dikerjakan jalan sebesar ......

Jawab: ______________________________________________________________________________

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licin

m2= 2 kg

m1= 1 kg

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8. Sebuah benda bermassa 6 kg bergerak pada bidang datar yang licin, kecepatan benda berkurang

dari 25 m/s menjadi 9 m/s setelah bergerak selama 4 sekon besar dan arah gaya mendatar yang

bekerja pada benda adalah ......

Jawab: ______________________________________________________________________________

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9. Sebuah elevator massanya 400 kg bergerak vertikal keatas dari keadaan diam dengan percepatan

tetap sebesar 2 m/s². Jika percepatan gravitasi 9,8 m/s², maka tegangan tali penarik elevator adalah .....

Jawab: ______________________________________________________________________________

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10. Benda yang massanya 10 diletakkan diatas lantai mendatar licin Jika benda ditarik dengan gaya

horisontal 35 N, maka besar percepatan yang timbul adalah ........

Jawab: ______________________________________________________________________________

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EVALUASI BAB 3 DINAMIKA GERAK

Pilihlah salah satu jawaban yang paling tepat !

1. Jika resultan gaya yang bekerja pada sebuah benda sama dengan nol, maka:

1) Benda tidak akan dipercepat

2) Benda selalu diam

3) Perubahan kecepatan benda nol

4) Benda tidak mungkin bergerak

Pernyataan yang benar ditunjukkan oleh nomor

a. (1), (2) dan (3)

b. (1) dan (3)

c. (2) dan (4)

d. (4) saja

e. (1), (2), (3) dan (4)

2. Perhatikan gambar dibawah, Jika kertas ditariik dengan cepat, maka silinder akan...

a. Ikut bergerak bersama kertas

b. Bergerak berlawanan dengan arah gerak kertas

c. Bergerak ke kanan

d. Bergerak ke kiri

e. Diam

3. Suatu benda bisa bergerak karena adanya...

a. Tenaga

b. Usaha

c. Energi

d. Gaya

e. Tenaga

4. Satuan percepatan adalah m/s2, jika dinyatakan dalam bentuk yang lain yaitu...

a. N/kg

b. Kg/N

c. m/s

d. cm/s

e. N/s2

5. Sebuah balok diletakkan diatas meja, balok tersebut bermassa m kg, besar gaya normal yang

bekerja pada balok karena dikerjakan olah meja adalah...


a. N=0

b. N=mg

c. N=m2

d. N=2m

e. N=g

6. Sebuah benda bermassa 10 kg bekerja resultan gaya sebesar 40 N. Maka percepatan yang dialami

benda adalah....

a. 1 m/s2

b. 2 m/s2

c. 3 m/s2

d. 4 m/s2

e. 5 m/s2

7. Sebuah benda bermassa 2 kg, mula-mula benda diam pada lantai datar dan licin, kemudian ditarik

dengan gaya konstan 8 N dengan arah mendatar, berapakah percepatan benda?

a. 0,25 m/s2

b. 2 m/s2

c. 4 m/s2

d. 8 m/s2

e. 16 m/s2

8. Sebuah mobil yang sedang melaju dengan kelajuan 36 km/jam tiba-tiba di rem hingga berhenti pada

jarak 10 m, jika gaya yang menghentikan mobil tersebut adalah 2.000 N, berapakah massa mobil

tersebut?

a. 5.000 kg

b. 4.000 kg

c. 3.000 kg

d. 2.000 kg

e. 1.000 kg

9. Balok bermassa 20 kg diletakkan diatas lantai mendatar yang licin, ditarik oleh gaya 50 N mendatar

ke kanan dan gaya 30 N mendatar ke kiri, maka balok akan bergerak dengan percepatan...

a. 1 m/s2 ke kanan

b. 1 m/s2 ke kiri

c. 2/3 m/s2 ke kanan

d. 3/2 m/s2 ke kiri

e. 2 m/s2 ke kanan

10. Perhatikan Gambar berikut ini

Gambar diatas menunjukkan 5 buah benda, diberi gaya yang berbeda-beda. Yang menghasilkan

percepatan benda paling besar adalah gambar nomor...

a. 1

b. 2


5 KgF=10 N

10 KgF=20 N

50 KgF=150 N

80 KgF=160 N

1 KgF=5 N

1 2 3 4 5

c. 3

d. 4

e. 5

11. Sebuah benda bermassa 5 Kg bergerak pada bidang datar yang licin, kecepatan benda bertambah

dari 4 m/s menjadi 8 m/s setelah menempuh jarak 8 m. Berapakah besar gaya yang menyebabkan

pertambahan kecepatan benda?

a. 100 N

b. 60 N

c. 30 N

d. 15 N

e. 10 N

12. Dua buah beban bermassa m1dan m2, dihubungkan dengan sebuah katrol (seperti pada gambar),

Jika m2>m1 percepatan gravitasi g dan gaya gesek diabaikan, besarnya tegangan tali T1 adalah....

a. m1g+m1a

b. m1g-m2g

c. m1g-m1a

d. m2g-m2a

e. m2g-m1a

13. Jika katrol licin dan percepatan gravitasi 10 m/s2, berapakah percepatan yang dialami benda?

a. 4 m/s2

b. 5 m/s2

c. 6 m/s2

d. 7 m/s2

e. 8 m/s2

14. Jika katrol licin sistem tersebut bergerak dengan percepatan 2 m/s2, Berapakah besar gaya

tegangan tali jika g= 10 m/s2

a. 10 N

b. 20 N

c. 30 N

d. 40 N

e. 50 N

15. Sebuah benda diikat dengan seutas tali dan digantung. Jika benda bermassa 5 kg, berapakah besar

gaya tegangan tali tersebut? (g = 10 m/s2)

a. 10 N

b. 20 N

c. 30 N

d. 40 N


T1T1

m2

m1

T

T

3 kg

Meja licin

2 kg

T

T

2 kg

Meja licin

10 kg

e. 50 N

16. Sebuah elevator massanya 300 kg, bergerak vertikal ke atas dari keadaan diam dengan percepatan

tetap sebesar 1 m/s2, jika g = 10 m/s2, berapakah besar tegangan tali penarik elevator?

a. 300 N

b. 600 N

c. 2700 N

d. 3000 N

e. 3300 N

17. Seorang anak berada didalam lift yang sedang bergerak keatas dengan percepatan 5 m/s2, jika

massa anak tersebut 40 kg, berapakah gaya normal yang bekerja pada anak tersebut? (g=10 m/s2)

a. 200 N

b. 400 N

c. 600 N

d. 660 N

e. 800 N

18. Pada lift yang mulai bergerak ke atas dengan percepatan 2 m/s2, berat seseorang yang berada

didalam lift tersebut adalah 480 N. Berapakah berat orang tersebut dalam keadaan normal (ketika lift

diam)...

a. 640 N

b. 560 N

c. 480 N

d. 400 N

e. 320 N

19. Sebuah balok bermassa 10 Kg berada diatas lantai yang licin, dan ditarik dengan gaya mendatar 2

N, berapakah besar percepatan yang dialami benda?

a. 0,2 m/s2

b. 1 m/s2

c. 2 m/s2

d. 4 m/s2

e. 5 m/s2

20. Sebuah benda yang bermassa 2 kg berubah kecepatanya dari 8 m/s menjadi 4 m/s dalam waktu 2

sekon kerena dikenai gaya tetap. Berapakah besara gaya tersebut?

a. – 2 N

b. – 4 N

c. – 6 N

d. – 8 N

e. – 10 N

21. Sebuah benda bermassa 2 kg dikenai sebuah gaya, menghasilkan percepatan 3m/s2. Jika gaya

tersebut bekerja pada benda bermassa 6 kg berapakah percepatan benda?

a. 1 m/s2

b. 2 m/s2

c. 3 m/s2


d. 4 m/s2

e. 5 m/s2

22. Perhatikan gambar berikut!

Besar dan arah percepatan yang dialami balok adalah......

a. 11 m/s2 ke kanan

b. 10 m/s2 ke kiri

c. 10 m/s2 ke kanan

d. 5 m/s2 ke kanan

e. 5 m/s2 ke kiri

23. Jika balok bermassa 5 kg berada pada lantai yang licin ditarik dengan gaya F=10 N, α= 300 (seperti

terlhat pada gambar), berapakah percepatan balok?

a. 1 m/s2

b. m/s2

c. m/s2

d. 2 m/s2

e. 5 m/s2

24. Sebuah benda bermassa 2 kg berada pada suatu bidang miring yang licin, jika α= 450 dan g=10

m/s2, berapakah percepatan balok?

a. 5 m/s2

b. m/s2

c. 5 m/s2

d. 2 m/s2

e. m/s2

25. Sebuah benda bermassa m bergerak pada bidang miring yang licin dengan sudut , jika percepatan

gravitasi g. Maka besar percepatan benda adalah...

a. 2 g sin

b. 2 g

c. g

d. g sin

e. g cos

26. Sebuah benda terletak pada bidang miring yang sudut kemiringanya 530. Jika massa benda 3 kg,

maka besar gaya normal yang bekerja pada benda tersebut adalah...

a. 10 N

b. 12 N

c. 16 N

d. 18 N

e. 24 N


m= 5 kg

F= 10 N

α

α

F1= 20 Nm= 2 kg

F3= 100 N

F2= 40 N

F4= 60 N

27. Jika kita memberikan gaya aksi ( dorongan pada suatu benda), maka kita akan merasakan gaya

reaksi dari benda tersebut. Gaya reaksi itu dapat kita rasakan dengan adanya...

a. Tarikan benda tersebut

b. Dorongan benda tersebut

c. Tarikan/ dorongan benda

d. Gaya normal

e. Semua benar

28. Berikut ini adalah contoh gaya aksi-reaksi, kecuali...

a. Gaya aksi-reaksi ketika tangan kita menekan meja

b. Benda yang digantung dengan tali pada atap

c. Gaya aksi-reaksi ketika kita menarik meja

d. Gaya aksi-reaksi pada gaya berat dan gaya normal

e. Gaya aksi-reaksi yan terjadi pada pelari yang start

29. Dua buah balok yang massanya sama, duhubungkan dengan seutas tali melalui sebuah katrol. Jika

sistem dalam keadaan setimbang, maka pasangan aksi-reaksi yang benar adalah...

a. T1dan T2

b. T1dan T4

c. T2dan T3

d. T5dan T6

e. W1dan W2

30. Dua buah benda A dan B berada diatas meja yang licin, saling dihubungkan dengan seutas tali

(seperti Pada gambar), massa A= 10 kg, massa B= 5 kg, benda B ditarik dengan gaya sebesar 30 N,

berapakah percepatan yang terjadi...

a. 1 m/s2

b. 2 m/s2

c. 3 m/s2

d. 4 m/s2

e. 5 m/s2

31. Seorang anak berada didalam lift yang bergerak ke bawah dengan percepatan 2 m/s2, jika massa

anak tersebut 30 kg, dan g= 10 m/s2. Berapakah gaya normal yang bekerja pada anak tersebut?

a. 360 N

b. 300 N

c. 240 N

d. 200 N

e. 60 N

32. Dua buah beban m1= 6 kg dan m2= 2 kg digantung dengan tali melalui sebuah katrol yang licin,

berapakah percepatan sistem tersebut?

a. 8 m/s2


T3

T1

W2

W1

T2

T4

T5

T6

T1T1

m2

m1

FA B

b. 7 m/s2

c. 6 m/s2

d. 5 m/s2

e. 4 m/s2

33. Sebuah balok bermassa 2 kg berada diatas lantai, jika g=10 m/s2, berapakah gaya normal yang

ditimbulkanya?

a. 5 N

b. 10 N

c. 15 N

d. 20 N

e. 30 N

34. Seseorang yang beratnya W berada didalam lift yang bergerak keatas dengan percepatan a, jika

percepatan gravitasi=g, berapakah besarnya gaya tegangan tali?

a. W

b.

c.

d.

e.

35. Sebuah benda pada saat t=0 sekon bergerak dengan kecepatan 50 m/s. Jika resultan dari gaya-

gaya yang bekerja pada benda sama dengan nol, maka kecepatan benda tersebut setelah bergerak

selama 10 sekon adalah...

a. 5.000 m/s

b. 500 m/s

c. 50 m/s

d. 25 m/s

e. 5 m/s

36. Sebuah benda bermassa 5 kg bergerak pada bidang datar yang licin dengan kecepatan 8 m/s dan

bertambah menjadi 10 m/s setelah menempuh jarak 10 m. Besar gaya mendatar yang menyebabkan

pertambahan kecepatan tersebut adalah...

a. 12 N

b. 10 N

c. 9 N

d. 8 N

e. 6 N

37. Sebuah benda bermassa 6 kg bergerak pada bidang datar yang licin, kecepatan benda berkurang

dari 25 m/s menjadi 9 m/s setelah bergerak selama 4 sekon. Berapakah besar dan arah gaya mendatar

yang bekerja pada benda tersebut?

a. 12 N searah dengan arah gerak


b. 12 N berlawanan dengan arah gerak

c. 24 N searah dengan arah gerak

d. 24 N berlawanan dengan arah gerak

e. 16 N berlawanan dengan arah gerak

38. Sebuah elevator massanya 400 kg bergerak vertikal ke atas dari keadaan diam dengan percepatan

tetap 2 m/s2. Jika percepatan gravitasi = 10 m/s2, maka tegangan tali elevator adalah...

a. 400 N

b. 800 N

c. 3120 N

d. 3920 N

e. 4720 N

39. Sebuah benda dengan massa m = 10 kg digantung dengan dua utas tali seperti pada gambar. Bila

benda diam dalam keadaan setimbang, berapakah tegangan tali T3?

a. 5 N

b. 10 N

c. 10 N

d. 50 N

e. 100 N

40. Dua buah massa m1= 5 kg dan m2= 3 kg dihubungkan dengan tali melalui sebuah katrol (seperti

pada gambar), anggap tali tidak bermassa, katrol licin, katrol tidak berputar, dan tegangan seluruh tali

sama, jika percepatan gravitasi= 10 m/s2, berapakah kecepatan kedua massa pada saat 2 detik setelah

benda bergerak dari keadaan diam?

a. 2,5 m/s

b. 5 m/s

c. 10 m/s

d. 12 m/s

e. 15 m/s

Essay

1. Bagaimanakah bunyi hukum I Newton?

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m

T1

T3

T2

300 450

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Secara matematis hukum II Newton dinyatakan dengan persamaan atau F=m.a, Jelaskan persamaan

tersebut?

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2. Resultan gaya pada huklum II Newton tidak sama dengan nol, apa maksudnya?

Jawab: ______________________________________________________________________________

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3. Bagaimanakah konsep gaya Aksi-reaksi menurut Hukum III Newton?

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4. Jelaskan perbedaan massa benda dan berat benda?


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5. Ketika kita naik sepeda pada saat jalan menurun, akan kiata rasakan laju sepeda semakin tinggi

walaupun pedal sepeda tidak dikayuh. Apa yang menyebabkan laju sepada semakin tinggi? Jelaskan.

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6. Sebuah benda yang diikatkan pada sebuah dinamometer (seperti pada gambar), menunjukkan

skala tertentu, menyatakan apa skala tersebut?

Jawab: ______________________________________________________________________________

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7. Sebuah balok kayu seberat 100 N diletakkan diatas lantai. Tentukan besar gaya normal jika:

a. Bagian atas balok ditekan dengan gaya F1= 30 N dan F2=20 N

b. Bagian atas balok ditekan dengan gaya F= 40 N dengan arah miring 300 ke bawah.

Jawab: ______________________________________________________________________________

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8. Sebuh balok berada diatas bidang miring yang membentuk sudut 300 terhadap arah mendatar, jika

massa balok= 30 kg, g=10 m/s2 dan balok tidak dikenai gaya luar, berapakah besarnya gaya normal

balok tersebut?

Jawab: ______________________________________________________________________________

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9. Seorang dengan massa 60 kg berada dalam lift yang sedang bergerak ke bawah dengan

percepatan 3 ms-2, desakan kaki orang pada lantai lift adalah?


Jawab: ______________________________________________________________________________

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10. Suatu benda mempunyai massa 2 kg dikenai gaya 100 N yang membentuk sudut 300 dengan arah

perpindahan benda. Tentukan percepatan benda!

Jawab: ______________________________________________________________________________

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11. Sebuah mobil yang bermassa 1000 kg bergerak dari keadaan diam dengan percepatan konstan ke

lajuan 10 m/s dalam waktu 5 sekon pada suatu jalan lurus. Berapakah besar gaya yang diperlukan untuk

mempercepat mobil tersebut?

Jawab: ______________________________________________________________________________

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12. Sebuah peti besar mempunyai massa 60 kg meluncur pada sebuah bidang miring licin yang

memiliki sudut kemiringan 300. Tentukan besarnya percepatan dan gaya normal!

Jawab: ______________________________________________________________________________

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13. Dua buah benda m1 dan m2 tersusun seperti gambar di bawah ini, m1= 10kg dan m2= 12kg. Jika massa

tali dan massa katrol, diabaikan dan koefisien gesekan kinetik antara tali dan

katrol, tentukan : (a) percepatan yang dialami oleh benda! (b) tegangan tali, (g

= 10ms-2).

Jawab: ______________________________________________________________________________

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14. Berapakah percepatan balok dan tegangan tali pada gambar di bawah ini?


m1

W1 W2

m2

a

45 N

Jawab: ______________________________________________________________________________

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REMIDIAL


1. Sebuah benda mempunyai massa 4 kg diberikan gaya 100 N searah dengan perpindahan benda,

tentukan percepatan benda!

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Secara matematis huukum II Newton dinyatakan dengan , Jelaskan maksud dari persamaan

tersebut?

Jawab: ______________________________________________________________________________

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2. Sebuah benda bermassa 4kg pada saat t=0. Sebuah gaya tunggal konstan yang horizontal (Fx)

bekerja sejauh pada benda tersebut. Setelah t = 3s, benda telah berpindah sejauh 2,25m. Berapakah

besar gaya Fx ini?

Jawab: ______________________________________________________________________________

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3. Seseorang bermassa 50 kg berdiri di dalam lift yang sedang bergerak ke atas dengan percepatan 5

m/s2. Jika percepatan gravitasi bumi adalah g = 10 ms-2, berapakah gaya tekan kaki orang tersebut pada

alas lift itu?

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4. Sebuah balok ditempatkan pada bidang miring licin. Sudut kemiringan bidang dan horizontal adalah

30o. Jika panjang bidang miring adalah 10 meter, tentukanlah waktu yang dibutuhkan oleh benda

tersebut saat tiba di ujung bidang miring!

Jawab: ______________________________________________________________________________

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5. Dua balok m1=2kg dan m2 = 5kg dihubungkan dengan katrol. Tidak ada gesekan antara m1 dan

alasnya. Jika g =10m s-2, tentukanlah: (a). percepatan yang dialami oleh m1 dan m2; (b) tegangan tali (T)!

Jawab: ______________________________________________________________________________

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6. Sebuah mobil dengan massa M, dari keadaan diam ke kelajuan 20 m/s dalam waktu 5s pada suatu

jalan lurus. Berapakah besar gaya yang mempercepat gerak mobil ini.

Jawab: ______________________________________________________________________________

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7. Sebuah benda bermassa 5kg (g = 9,8 ms-2) digantungkan dengan seutas tali, tentukanlah gaya

tegangan tali pada saat itu sistem dalam keadaan diam.

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8. Dua buah benda m1 dan m2 tersusun seperti gambar di bawah ini, m1= 1kg dan m2= 2kg. Jika massa tali

dan massa katrol, diabaikan dan tidak ada gesekan antara tali dan katrol, tentukan percepatan yang

dialami oleh masing-masing benda! (g = 10ms-2).

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m1

W1 W2

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9. Seseorang ber massa 50kg berada di dalam sebuah lift yang sedang bergerak dengan percepatan 5

m/s2 ke bawah. Tentukanlah tekanan kaki orang terhadap alas lift! (g=10 m/s2).

Jawab: ______________________________________________________________________________

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10. Sebuah benda digantung dengan seutas tali. Dalam keadaan diam, tegangan talinya adalah 100N,

(g=10ms-2). Jika tali hanya mampu menahan tegangan sebesar 180N, dengan percepatan maksimum

berapakah benda tersebut dpt ditarik ke atas, tepat pada saat tali akan putus?

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11. Sebuah benda bermassa 10 kg (g = 10 ms-2) digantungkan dengan seutas tali, tentukanlah gaya

tegangan tali pada saat sistem bergerak ke atas dengan percepatan 6 ms-2.

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12. Sebuah benda bermassa 5kg (g = 10 ms-2) digantungkan dengan seutas tali, tentukanlah gaya

tegangan tali pada saat itu:


T1 T2

a. Sistem dalam keadaan diam

b. Sistem bergerak ke atas dengan percepatan 5 ms-2.

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13. Tiga benda masing-masing m1 = 1kg, m2 = 2kg, dan m3 = 3kg, berada pada bidang datar

licin, dihubungkan dengan tali seperti pada gambar berikut. Kemudian, sistem tersebut ditarik dengan

gaya 24 N. Tentukanlah besarnya tegangan tali T1 dan T2 !

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14. Seseorang ber massa 50kg berada di dalam sebuah lift yang sedang bergerak dengan

percepatan 3 ms-2 ke bawah. Tentukanlah tekanan kaki orang terhadap alas lift! (g=10ms-2).

Jawab: ______________________________________________________________________________

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PENGAYAAN


1. Seorang dengan massa 60 kg berada dalam lift yang sedang bergerak ke bawah dengan

percepatan 3 ms-2. Berapakah desakan kaki orang pada lantai lift?

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2. Sewaktu berada di dalam lift yang diam, berat Sandi adalah 500 N. Percepatan gravitasi = 10 m s–2.

Sewaktu lift dipercepat, tegangan tali menjadi 750 N. Dengan demikian percepatan lift adalah …

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3. Sebuah massanya 1 kg balok diletakkan di atas bidang miring licin dengan sudut kemiringan (α) =

30o, sehing-ga benda bergerak dengan percepatan konstan. Bila g = 10 m s–2, maka gaya penggerak

balok tersebut adalah …

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4. Benda bermassa 4 kg terletak pada bidang miring seperti tampak pada gambar di bawah ini.

Jika koefisien gesek-an statik antara balok dan bidang miring adalah 15 √3 dan g = 10 m s–2, maka

resultan gaya yang meluncurkan benda adalah …

30o

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5. Balok A yang massanya 5 kg, diletakkan pada bidang datar yang licin, balok B yang massanya 3 kg

digantung dengan tali, dan dihubungkan dengan balok A melalui sebuah katrol, jika g = 10 m/s2 tentukan

percepatan balok tersebut?

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6. Sebuah benda dijatuhkan dari ujung sebuah menara tanpa kecepatan awal. Setelah 2 detik benda

sampai di tanah (g = 10 m s2). Tinggi menara tersebut …

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7. Sebuah benda jatuh bebas dari ketinggian 40 m di atas tanah. Bila massa benda 2 kg dan g = 10 m

s–2 maka energi kinetik tepat 20 m di atas tanah adalah …

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8. Benda bermassa 5 kg dilempar vertikal ke atas dengan kecepatan awal 10 m s–1. Besarnya energi

potensial dititik tertinggi yang dicapai benda adalah … (g = 10 m s–2)

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9. Buah kelapa dan buah mangga jatuh bersamaan dari ke-tinggian h1 dan h2. Bila h1 : h2 = 2 : 1, maka

perbanding-an waktu jatuh antara buah kelapa dengan buah mangga adalah …

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10. Sebuah benda dilemparkan vertikal keatas dari suatu tempat yang tingginya 20 meter di atas tanah

dengan kecepatan 40 m s–1. Jika g = 10 m s–2 maka tinggi maksimum yang dapat di capai benda dari

permukaan tanah adalah …

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11. Balok-balok A, B dan C terletak pada bidang datar yang licin. Jika Massa A= 5 kg, massa B= 3 kg

dan massa C= 2 kg, dan F= 10 N, Maka perbandingan besar tegangan tali antara A dan B dengan besar

tegangan tali antara B dan C adalah…

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A B C F

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12. Sebuah balok dengan massa 5 kg ditarik dengan seutas tali membentuk sudut 300 terhadap arah

mendatar. Jika gaya penarik balok tersebut sebesar 20 N dan masa tali diabaikan, maka percepatan

balok adalah…

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13. Gaya F sebesar 12 N bekerja pada sebuah benda yang massanya m1, menyebabkan percepatan m1


sebesar 8 m/s2. Jika F bekerja pada benda yang bermassa m2, maka percepatan yang ditimbulkan

adalah 2 m/s2. Jika F bekerja pada benda yang bermassa m1+m2, maka percepatan benda ini adalah…

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14. Didalam sebuha lift ditempatkan sebuah timbangan badan. Saat lift dalam keadaan diam seseorang

minimbang bandanya, didapatkan bahwa berat badan orang tersebut 500 N. Jika lift bergerak ke atas

dengan percepatan 5 m/s2, g=10 m/s2, maka berat orang tersebut saat ditimbang menjadi…

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15. Sebuah helikopter bermassa 300 kg bergerak vertikal ke atas dengan percepatan 2 m/s2. Seorang

tentara bermassa 60 kg memanjat tali yang menjulur dengan kecepatan tetap 1 m/s relatif terhadap

helikopter, berapakah gaya tegangan tali saat itu?

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Dinamika Gerak smstr 1

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