Molecular Physics | Thermodynamics Answers

Over the course of the day you do 1.5Mj of mechanical work and lose 28.5Mj of heat while maintaining a constant body temperature.

What mass of food with an energy content of 50 Mj kg -1 would you need to invest in order to avoid weight loss? (2sf and in kg)

What is the momentum of a 12.2 kg turtle swimming upstream with a speed of 3.3 m/s.

Two men are standing on the same side of a high wall and at the same distance from it such that they are 400 m apart. when one man fires a pistol, the other hears the first report 1.2 s after seeing the flash and the second report 0.5 s after the first. Explain why he hears two reports and calculate the (a) velocity of sound in air (b) perpendicular distance of the men from the wall?

Why does it requires great amount of heat to increase the temperature of 10kg water from 10° to 20°

Steam at 5 bar and 250 Deg is contained in

a rigid vessel of volume 2.2 m, The vessel

is cooled until the steam is just dry saturated.

Calculate the heated rejected, the change in

entropy, the final pressure and the mass of

the steam.

A mass of 0.05 kg of a perfect gas with a

molar mass of 70 kg/kmol, occupying a

volume of 0.03 m at 1.025 bar,

is

compressed

reversibly until the pressure is

6.15 bar. Calculate the final temperature, the

work done on the prefect gas and the heat

supplied:

I. When the process is according to a law

II. When the process is isothermal

II. When the process takes place in a

perfectly thermally insulated cylinder

Take cy = 395.93 J/kg.K

If 10-7 J of heat is added to a system w is so large that its temperature () /" does not change, by what factor will the number of accessible states of the system increase if the temperature is 30 K? 

The power developed by a gas turbine is 15000 kW. Gases flow through the turbine of the gas turbine unit at 20 kg/s. The specific enthalpies of the gases at the inlet and the outlet of the turbine are 1300 kJ/kg and 400 kJ/kg respectively. The velocities of the gases at the inlet and the outlet are 65 m/s and 155 m/s respectively.

(a) Draw a schematic diagram of the turbine and label the flows in and out of it. (2 marks)

(b) What is the purpose of a gas turbine? How does irreversibility affect the performance of a gas turbine? (4 marks)

(c) Explain the equation which can be used to assess changes in energy in the turbine. (3 marks)

(d) Calculate the rate at which heat is rejected from the turbine. (11 marks)

(e) Calculate the area of the turbine inlet pipe if the specific volume of the gases at inlet is 0.6 m3 /kg. (5 marks)

1. (a) Explain what is meant by a reversible process. Why are real processes not reversible? (5 marks)

(b) A cylinder contains a unit mass of a fluid. The initial pressure is 10 bar and the initial volume is 0.03 m^3 . The fluid expands reversibly behind a piston according to the equation pV^2 = constant until the volume is doubled. The fluid is then cooled reversibly at constant pressure until the piston goes back to its initial position. Heat is then supplied with the piston firmly locked in position until the pressure increases and reaches the initial value of 10 bar.

(i) Sketch the cycle on a labelled pressure-volume diagram. (5 marks)

(ii) Calculate the net work done by the fluid. (15 marks)

a.What is meant by reversible process?