Search results

  1. P

    Thermodynamics - efficiency from pv diagram

    i think it is a ratio of e_carnot/e where e = 17% ^^^^that ratio is correct, e_carnot/e = 83.33/17 = 4.90
  2. P

    Thermodynamics - efficiency from pv diagram

    let 6atm, 2L = 1, 6atm,6L = 2, 3atm, 6L = 3, 3atm, 2L = 4: 1-->2 isobaric expansion Q = nC_pT = n(5R/2)(PV/nR) = 5/2(PV) = 5/2(607950)(0.006-0.002) = 6079.5 2-->3 isovolumetric compression Q = n(3R/2)(PV/nR) = 3/2(PV) = 3/2(303975-607950)(0.006) = -2735.8 3-->4 isbaric compression Q =...
  3. P

    Thermodynamics - efficiency from pv diagram

    i still can't seem to get it, how do i find the q for the isvolumetric paths when Q = 3/2(P*deltaV) where pressure changes over each pf the two isovolumetric paths? help please
  4. P

    Thermodynamics - efficiency from pv diagram

    i tried what you said and got Q = 6079.5 joules for top isobaric, and Q = -1823.85 joules for bottom isobaric so e = W/Q_h = 1215/(6079.5-1823.85) = 1215/4255.65 = 28.5% which was wrong, what now?
  5. P

    Thermodynamics - engine efficiency

    oh i should've been more specific, i do know people who go to umbc, i am actually posting on behalf of one my old school mates who goes to umbc, he works nights and cant get stuff done btw 24.3 worked
  6. P

    Thermodynamics - engine efficiency

    nah i go to old dominion, i already tried W/Q_h where W = 350 joules, my original Q_h was wrong i used temp not Q, as for Net = 691.5-748.3+748.3-345.8 = 345.8, so should e = 350/345.8 = 101.2 % or 350/350 = 100%? or should it be Q_h = 691.5 + 748.3 = 1439.8 so e = 350/1439.8 = 24.3%?
  7. P

    Thermodynamics - engine efficiency

    using (Q_h - Q_c)/Q_h = (600 - 300)/600 = 50% was not correct? what am i doing wrong?
  8. P

    Thermodynamics - engine efficiency

    the question wants me to use a ratio of work and heat energy though, why should i use (Q_h - Q_c)/Q_h? so should i be getting 50% then is use the efficiency equation you suggest?
  9. P

    Thermodynamics - efficiency from pv diagram

    Homework Statement Determine the efficiency for the cycle shown in the figure, using the definition. Assume that the gas in the cycle is ideal monatomic gas. Compare with the efficiency of a Carnot engine operating between the same temperature extremes. see attachment Homework...
  10. P

    Thermodynamics - engine efficiency

    Homework Statement A reversible engine contains 0.20 mol of ideal monatomic gas, initially at 600 K and confined to 2.0 L. The gas undergoes the following cycle: Isothermal expansion to 4.0 L. Isovolumic cooling to 300 K. Isothermal compression to 2.0 L. Isovolumic heating to 600 K...
  11. P

    Thermodynamics - hot item placed in water

    sorry to double post, just wanted to let you all know that the above values i got were in fact correct. thanks for the help
  12. P

    Thermodynamics - hot item placed in water

    using the above equation i got this: Tf_w = Tf_al = 24.5 = 24.5 + 273 = 297.5 kelvin Ti_w = 19 = 19 + 273 = 292 kelvin find Ti_al [(12)(4184)(297.5-292)]_water + [(0.9)(900)(297.5 -Ti)]_aluminum = 0 271644 + 240975 - 810Ti = 0 810Ti = 517119 Ti = 638.41 kelvin, so for part one Ti in celsius =...
  13. P

    Thermodynamics - hot item placed in water

    is that the same case for the water, so instead of 5.5 it should also be T = (24.5 - Ti), what happens to the 19 degrees stated in the problem?
  14. P

    Thermodynamics - hot item placed in water

    i see what you're saying topher, so T should then be (24.5 - Ti)?
  15. P

    Thermodynamics - hot item placed in water

    so should T actually be (Tf - Ti) where Tf is final temp and Ti is the initial temp? or should T just become deltaT = change in temp? should i even have two unknowns for temperature? actually it should have been 24.5 - 19 = 5.5, not 5. how do i use the temperature change (5.5)? am i supposed...
  16. P

    Thermodynamics - hot item placed in water

    Homework Statement A 900 g aluminum pan is removed from the stove and plunged into a sink filled with 12.0 L of water at 19.0 degrees. The water temperature quickly rises to 24.5 degrees. What was the initial temperature of the pan in degrees C? What was the initial temperature of the...
  17. P

    Thermodynamics - ice->water->steam

    Homework Statement A 8.0 g ice cube at -30 C is in a rigid, sealed container from which all the air has been evacuated. How much heat is required to change this ice cube into steam at 240 C? Homework Equations Q_net = 0 where Q is heat C1 = Specific heat capacity, ice: 2.050...
  18. P

    Normal and shear stresses due to tension

    Homework Statement at a point in a stressed body, there are normal stresses of 95 MPa (tension) on a vertical plane and 125 MPa (tension) on a horizontal plane. determine the normal and shear stresses at this point on the inclined plane a-b (please see attachment) the solution should be...
  19. P

    Ideal gas law - isovolumetric problem

    yes i tried it with 293 as the denominator. it was correct thanks for your help
  20. P

    Simple temperature conversion

    thanks, it was correct
  21. P

    Simple temperature conversion

    so 0 deg celsius = 32 fahr, 43.8 deg celsius = 110.84 fahr so the fahrenheit difference is 110.84 - 32 = 78.84 fahr. thus the temp when the desired temp increase has been achieved is 62.7 + 78.84 = 141.54 fahrenheit correct?
  22. P

    Ideal gas law - isovolumetric problem

    the thing is when tried (313p_1)/292, it was incorrect and it stated that "your answer either contains an incorrect numerical multiplier or is missing one." noticed how i entered the denominator as 292 as opposed to 293, would that be the reason why it is incorrect?
  23. P

    Simple temperature conversion

    i am still confused. isn't 110.84 the fahrenheit temperature difference equivalent to 43.8 celsius? so couldn't i chose 0 deg fahr. as the initial and 110.84 deg fahr. as the final temperatures? what formula should i be using, is the one i listed in the original post the correct one?
  24. P

    Simple temperature conversion

    do you mean i do the difference between 173.54 - 62.7 = 110.84? isn't that the change fahrenheit?
  25. P

    Ideal gas law - isovolumetric problem

    Homework Statement A gas sample enclosed in a rigid metal container at room temperature (20 C) has an absolute pressure p_1. The container is immersed in hot water until it warms to 40 C. What is the new absolute pressure p_2? Express your answer in terms of p_1 Homework Equations PV = nRT...
  26. P

    Simple temperature conversion

    Homework Statement i feel rather stupid posting this, but i can't seem to figure it out: increase a sample by 43.8 degrees celsius. if the sample is already 62.7 degrees fahrenheit, what is the temperature in degrees fahrenheit when the desired temperature increase has been achieved...
  27. P

    Shearing stress - timber truss

    after checking the solutions, the dimension for a should be 53.3mm, i am getting 80mm. after doing the method of joints here are my values for the reactions F_BA = F_BC = 9kN F_BD = 18kN F_DA = F_DC = F_CD = 12kN Cy = Ay = -7.94kN see attachment for corrected free body diagram and angles...
  28. P

    Shearing stress - timber truss

    when i solve for the tensile force in the bottom chord, is the best way to do this is: - treat the bottom chord as the sum of the two 2m pieces --> find reactions/tensile in each 2m portion and then sum them is the average shearing stress a component of an angle, there is none given or am i...
  29. P

    Shearing stress - timber truss

    when i solve for the tensile force in the bottom chord, is the best way to do this is: - treat the bottom chord as the sum of the two 2m pieces is the average shearing stress a component of an angle, there is none given or am i meant to deduce the angle from finding out the reactions etc?
Top