personal letter

an example of personal letter

Dear Ajeng,

How have you been? I hope you and your family are always fine. I am here fine too. By the way, have you got your last examination score for your second semester? I hope you get your best score for all lesson. How about your second semester holiday? When will it come? And where will you spend it?

I want to invite you to join in my holiday. My dearest friends and I are going to hike the Welirang Mountain on 15-17 June 2012. Usually when we are on the mountain, we feel a very different felling. I mean it is such as a peace place. Maybe, because the weather is very nice and a very beautiful scenery there. And also a cold fog. It is an awesome thing that we could not find in our city. It will be more exited if you could join us ! So, please join it, won`t you? I hope you can. You have not ever hiked, haven`t you? 

Okay, I think that`s all for my letter. Please replay this letter soon. I am waiting for your reply.

Best wishes,

( name )

opinion paragraph

this is an example of opinion paragraph

Saving Resources

         We should save resources by taking shorter baths, separating rubbish, and using recycle bags. I think if we take shorter baths, we will be able to save a lot of water. Water is so important for everyone, so we should conserve whenever we can. Some families reuse their bath water in the washing  machine. That’s a great idea. We can also help save the planet by separating our garbage. This is a good way to recycle materials. If we do this, we can keep our environment cleaner. We should recycle almost everything we use. We should challenge ourselves to do this. Finally, we should never accept extra packaging in the stores. We should always have our recycle bag ready. When the shop assistant starts to package everything in one or two or three ways, we can hole up our bag and say, “This is enough. Thank you”.  I think Indonesia should ban plastic bags entirely. We must work very hard to live on this earth in an ecologically friendly way. It is our responsibility.

Advantages and disadvantages paragraph

well, this is an example of  Advantages and disadvantages paragraph.

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Coffee

Coffee is one of the highly preferred beverage by all people. Indonesian people are very familiar with it. The main substance of coffee is caffeine. Although caffeine known  as a dangerous substance,  in fact, caffeine has some advantages. Such as stimulating the heart, pain relief and if caffeine is consumed in low doses, caffeine can be used as a generator of stamina. And for disadvantages of coffee on our  health  are dependency effects , increasing the risk of stroke, damage to blood vessel walls, and insomnia. coffee sensation is incredible. but keep in mind, for not more than three cups in a day, there is no harm for you to enjoy it.

contoh soal dan pembahasan thermodinamika

1. Suatu gas memiliki volume awal 2,0 m3 dipanaskan dengan kondisi isobaris hingga volume akhirnya menjadi 4,5 m3. Jika tekanan gas adalah 2 atm, tentukan usaha luar gas tersebut!

(1 atm = 1,01 x 105 Pa)

 Kunci : 5,05 x 105 joule

2. 1,5 m3 gas helium yang bersuhu 27oC dipanaskan secara isobarik sampai 87^oC. Jika tekanan gas helium 2 x 105 N/m2 , gas helium melakukan usaha luar sebesar….

A. 60 kJ

B. 120 kJ

C. 280 kJ

D. 480 kJ

E. 660 kJ

(Sumber Soal : UMPTN 1995)

Kunci : 60 kJ

3. 2000/693 mol gas helium pada suhu tetap 27oC mengalami perubahan volume dari 2,5 liter menjadi 5 liter. Jika R = 8,314 J/mol K dan ln 2 = 0,693 tentukan usaha yang dilakukan gas helium!

Kunci : 4988,4 joule

4. Mesin Carnot bekerja pada suhu tinggi 600 K, untuk menghasilkan kerja mekanik. Jika mesin menyerap kalor 600 J dengan suhu rendah 400 K, maka usaha yang dihasilkan adalah….

A. 120 J

B. 124 J

C. 135 J

D. 148 J

E. 200 J

(Sumber Soal : UN Fisika 2009 P04 No. 18)

Kunci : 200 J

5. Diagram P−V dari gas helium yang mengalami proses termodinamika ditunjukkan seperti gambar berikut!

Usaha yang dilakukan gas helium pada proses ABC sebesar….

A. 660 kJ

B. 400 kJ

C. 280 kJ

D. 120 kJ

E. 60 kJ

(Sumber Soal : UN Fisika 2010 P04 No. 17)

Kunci : 400kJ

6. Suatu mesin Carnot, jika reservoir panasnya bersuhu 400 K akan mempunyai efisiensi 40%. Jika reservoir panasnya bersuhu 640 K, efisiensinya…..%

A. 50,0

B. 52,5

C. 57,0

D. 62,5

E. 64,0

 (Sumber Soal : SPMB 2004)

Kunci : 62,5%

7. Perhatikan gambar berikut ini!

Jika kalor yang diserap reservoir suhu tinggi adalah 1200 joule, tentukan :

a) Efisiensi mesin Carnot

b) Usaha mesin Carnot

c) Perbandingan kalor yang dibuang di suhu rendah dengan usaha yang dilakukan mesin Carnot

d) Jenis proses ab, bc, cd dan da

kunci : 40%, 480 joule, 3 : 2

Soal No. 8

Suatu gas ideal mengalami proses siklus seperti pada gambar P − V di atas. Kerja yang dihasilkan pada proses siklus ini adalah….kilojoule.

A. 200

B. 400

C. 600

D. 800

E. 1000

Kunci : 400kJ

pembahasan 

      Pembahasan no 1

V2 = 4,5 m³  V1 = 2,0 m³

P = 2 atm = 2,02 x 10⁵ Pa

Isobaris → Tekanan Tetap

W = P (ΔV)

W = P(V2 − V1)

W = 2,02 x 10⁵ (4,5 − 2,0) =  5,05 x 10⁵ joule

      Pembahasan no 2

V₁ = 1,5 m³

T₁ = 27^oC = 300 K

T₂ = 87^oC = 360 K

P = 2 x 10⁵ N/m2

W = PΔV

Mencari V₂ :

V₂/T₂ = V₁/T₁

V₂ = ( V₁/T₁ ) x T₂ = ( 1,5/300 ) x 360 = 1,8 m³

W = PΔV = 2 x 10⁵(1,8 − 1,5) = 0,6 x 10⁵ = 60 x 10³ = 60 kJ

      Pembahasan no 3

n = 2000/693 mol

V₂ = 5 L

V₁ = 2,5 L

T = 27^oC = 300 K

Usaha yang dilakukan gas :

W = nRT ln (V₂ / V₁)

W = (2000/693 mol) ( 8,314 J/mol K)(300 K) ln ( 5 L / 2,5 L )

W = (2000/693) (8,314) (300) (0,693) = 4988,4 joule

      Pembahasan no 4

η = ( 1 − Tr / Tt ) x 100 %

Hilangkan saja 100% untuk memudahkan perhitungan :

η = ( 1 − 400/600) = 1/3

η = ( W / Q1 )

1/3 = W/600

W = 200 J

      Pembahasan no 5

W_AC = W_AB + W=

W_AC = 0 + (2 x 105)(3,5 − 1,5) = 4 x 10⁵ = 400 kJ

      Pembahasan no 6

Data pertama :

η = 40% = 4 / 10

Tt = 400 K

Cari terlebih dahulu suhu rendahnya (Tr) hilangkan 100 % untuk mempermudah perhitungan:

η = 1 − (Tr/Tt)

4 / 10 = 1 − (Tr/400)

(Tr/400) = 6 / 10

Tr = 240 K

Data kedua :

Tt = 640 K

Tr = 240 K (dari hasil perhitungan pertama)

η = ( 1 − Tr/Tt) x 100%

η = ( 1 − 240/640) x 100%

η = ( 5 / 8 ) x 100% = 62,5%

      Pembahasan no 7

a) Efisiensi mesin Carnot

Data :

Tt = 227_oC = 500 K

Tr = 27_oC = 300 K

η = ( 1 − Tr/Tt) x 100%

η = ( 1 − 300/500) x 100% = 40%

b) Usaha mesin Carnot

η = W/Q₁

4/10 = W/1200

W = 480 joule

c) Perbandingan kalor yang dibuang di suhu rendah dengan usaha yang dilakukan mesin Carnot

Q₂ = Q₁ − W = 1200 − 480 = 720 joule

Q₂ : W = 720 : 480 = 9 : 6 = 3 : 2

d) Jenis proses ab, bc, cd dan da

ab → pemuaian isotermis (volume gas bertambah, suhu gas tetap)

bc → pemuaian adiabatis (volume gas bertambah, suhu gas turun)

cd → pemampatan isotermal (volume gas berkurang, suhu gas tetap)

da → pemampatan adiabatis (volume gas berkurang, suhu gas naik)

      Pembahasan no 8

W = Usaha (kerja) = Luas kurva siklus = Luas bidang abcda

W = ab x bc

W = 2 x (2 x 105) = 400 kilojoule