Piston problem including force and work

  • #1
jessiemay1993
3
0
The problem given says: A cylinder has a cross-sectional area of 0.02 m^2. How much work is done by a gas in the cylinder if the gas exerts a constant pressure of 7.8x10^5 Pa on the piston, moving it a distance of 0.06 m?



I figured I needed to find the work, but I didn't have the force.

So I tried the equation Pressure*Area=Force

Then to get work, I used the equation Force*distance=Work


For the force, I got 15600. I then plugged that into the second formula as force and got 936. I have a really strong feeling it's not correct. My answer choices are as followed: A. 6.5*10^2 J B. 9.4*10^2 J C. 6.5*10^8 J and D. 9.4*10^8 J

I'm really confused on this and would really appreciate the help. My teacher doesn't really teach us what we need to know. Just throws it up on the board, briefly talks about it and expects us to learn from that. So would someone also help me understand Thermodynamics? It would be greatly appreciated :]

Thank you in advance,
Jessica
 

Answers and Replies

  • #2
SammyS
Staff Emeritus
Science Advisor
Homework Helper
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Change you answer to scientific notation or the 4 choices to standard notation.

A. 6.5×102 J B. 9.4×102 J C. 6.5×108 J and D. 9.4×108 J

Your answer is very close to one of them.
 
  • #3
jessiemay1993
3
0
Wow! Thank you so much :]
 
  • #4
gomunkul51
275
0
Also: d(Work) = pressure*d(volume) ;)
 
  • #5
jessiemay1993
3
0
Also: d(Work) = pressure*d(volume) ;)


What??? Now I'm super confused o_O
 
  • #6
Andrew Mason
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What??? Now I'm super confused o_O
Don't be confused. It just arithmetic:

[tex]W = F \times \Delta d = (P \times A) \times \Delta d = P \times (A \times \Delta d) = P \times (\Delta V)[/tex]

where [itex]\Delta V[/itex] is the change in volume of the gas.

AM
 
  • #7
gomunkul51
275
0
@jessiemay1993: if you want to be confused, take Engineering Thermodynamics ;)

Andrew Mason <--- what he said ;)
 
  • #8
ashishsinghal
462
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what answer you got was with the assumption that the pressure remains constant. but actually it does not as the pressure and volume are inter related. but since you have no initial value of he volume the assumption may be correct.
 
  • #9
ashishsinghal
462
0
what equation gomunkul51 has written is the same as yours when keeping pressure constant. its just written in a different way. so no need to be confused
 

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