Unit Conversion: What went wrong?

AI Thread Summary
The discussion centers on a unit conversion error in calculating the mass required for a dead-weight gauge measuring pressures up to 3000 atm. The initial calculation yielded approximately 2.627 lbm, while the correct answer is 1000.7 lbm. Participants highlight the need to consider the distinction between pound-force (lbf) and pound-mass (lbm), emphasizing the role of gravitational acceleration in the conversion. Clarifications regarding the proper units and calculations are requested, with some confusion about the application of gravitational force. Ultimately, the conversation underscores the importance of accurate unit conversions in physics problems.
xiangru119
Messages
4
Reaction score
0

Homework Statement


Pressures up to 3000 atm are measured with a dead-weight gauge. The piston diameter is 0.17 (in). What is the approximate mass in (lbm) of the weights required?

The Attempt at a Solution


Abs. pressure = Gauge pressure + Atmospheric pressure
= 3000 atm + 1 atm
= 3001 atm * 14.696 psi/atm
= 44102.696 psi
A = pi*D2/4
= 0.023 in2
P = F/A
P*A = mg
44102.696*0.023 = m * 32.174 ft/s2 (12 in./1 ft)
m= 2.627 lbm

4. The actual answer: 1000.7 lbm. So can anyone point out my error?
Any help would be appreciated. Thank you.
 
Physics news on Phys.org
A mass of 1 lbm weighs 1 lbf in standard gravitational field.

<br /> 4.41 \times 10^{4} \, \frac{\mathrm{lb}}{\mathrm{in}^{2}} \times (2.3 \times 10^{-2} \, \mathrm{in}^{2}) = 1.01 \times 10^{3} \, \mathrm{lb}<br />
 
Dickfore said:
A mass of 1 lbm weighs 1 lbf in standard gravitational field.

<br /> 4.41 \times 10^{4} \, \frac{\mathrm{lb}}{\mathrm{in}^{2}} \times (2.3 \times 10^{-2} \, \mathrm{in}^{2}) = 1.01 \times 10^{3} \, \mathrm{lb}<br />

Hi, the answer obtained from this should be equivalent to pound force. How about the accelerate force of gravity? Thanks for your comment.
 
xiangru119 said:
Hi, the answer obtained from this should be equivalent to pound force. How about the accelerate force of gravity? Thanks for your comment.

I don't know what you are talking about. I was not supposed to solve even this much I think. Please use proper English to communicate your ideas.
 
I apologise for my broken English. I mean the answer obtained (1.01x10^3 lb) might be lbf instead of lbm. I think acceleration of gravity needed to be taken into account in order to get lbm.
 
But, it is taken into account. Did you read this:
Dickfore said:
A mass of 1 lbm weighs 1 lbf in standard gravitational field.
 
Ok, I will think about it. Thanks
 

Similar threads

Back
Top