Molecular Physics | Thermodynamics Answers

If the temperature of a hot reservoir is 400K, what must the exhaust temperature be so that the efficiency of an ideal heat engine is 25%?

If all the energy of a 20-g bullet travelling at 1km/s is converted into heat, how many calories are generated?

A gas expands from I to F in the figure. The energy added to the gas by heat is 423 J when the gas goes from I to F along the diagonal path. What is the change in internal energy of the gas?

Answer in units of J

There are 400kf/min of water being handled by a pump. The lift us firm 20-m deep well and the delivery velocity ks 15m/s. Find (a) the change in potential energy, (b) kinetic energy, (c) the required power of the pumping unit; g= 9.81m/s²

What is the temperature gradient of 8.0 cal per second per cm with 210 Wk

Oxygen ( molecular weight 32) is compressed reversibly and polytropically in a cylinder

from 1.05 bar, 15oC to 4.2bar in such a way that one- third of the work input is rejected

as heat to the cylinder walls . calculate the final temperature of the oxygen. Assume

oxygen to be a perfect gas and take Cv = 0.649kJ/kg.K

0.05 kg of carbon dioxide (molecular weight 44), occupying a volume of 0.03m3 at

1.025bar , is compressed reversibly until the pressure is 6.15bar. calculate the final

temperature the work done on the CO2 and the heat flow to or from the cylinder walls ,

1- when the process is according to the law p.ν1.4 = constant , 2- when the process is

isothermal , assume carbon dioxide to be a perfect gas , and take γ = 1.3

Oxygen, O2, at 200 bar is to be stored in a steel vessel at 20oC the capacity of the vessel

is 0.04m3

. Assuming that O2 is a perfect gas, calculate the mass of oxygen that can be

stored in the vessel. The vessel is protected against excessive pressure by a fusible plug

which will melt if the temperature rises too high. At what temperature must the plug

melt to limit the pressure in the vessel to 240bar? The molecular weight of oxygen is 32

(10.5 kg; 78.6oC)

A heat exchanger wall consists of a copper plate 20 mm thick. The heat transfer

coefficients on the two sides of the plate are 2700 and 7000 W/m2K, corresponding to

fluid temperatures of 92 °C and 32 °C, respectively. Assuming that the thermal

conductivity of the wall is 375 W/mK,

a. Calculate the surface temperatures in °C, and

b. Calculate the overall heat transfer in W/m2K.

3.A heat engine makes use of the thermal cycle shown. The working fluid is 3 grams of nitrogen, an ideal diatomic gas. There are two isobaric and two isochoric processes:

p1 = 1×10⁶ Pa, p2 = 2×10⁶ Pa

V1 = 500 cm³, V2 = 1000 cm³.

a) What is the temperature, T, of the gas at point 4 (p1, V1)?

A.  T = 120 K

B.  T = 561 K

C.  T = 842 K

b) How much work, Wby, does the gas do in the 1→2 process?

 A.  Wby = -1000 J

B.  Wby = -500 J

C.  Wby = 500 J

D.  Wby = 1000 J