Try out these questions on Thermodynamics and test your competency level in the subject for GATE Mechanical and UPSC ESE exams. 

Q1) A 110-mm-diameter cylinder contains 100 cm3 of water at 60°C. A 50-kg piston sits on top of the water. If heat is added until the temperature is 200°C, fi nd the work done.

Q2) Energy is added to a piston-cylinder arrangement, and the piston is withdrawn in such a way that the temperature (i.e., the quantity PV) remains constant. The initial pressure and volume are 200 kPa and 2 m3 , respectively. If the fi nal pressure is 100 kPa, calculate the work done by the ideal gas on the piston.

Q3) A 100 kg mass drops 3m, resulting in an increased volume in the cylinder shown of 0.002 m3. The weigh and the piston maintain a constant gage pressure of 100 kPa. Determine the net work done by the gas on the surroundings. Neglect all friction.

Q4) The air in a 10-cm-diameter cylinder shown is heated until the spring is compressed 50 mm. Find the work done by the air on the frictionless piston. The spring is initially unstretched, as shown.

 Q5) As shown in the figure, a cylinder of compacted scrap metal measuring 2 m in length and 0.5 m in diameter is suspended from a spring scale at a location where the acceleration of gravity is 9.78 m/s2. If the scrap metal density varies with position, z, in m, according to , determine the reading of the scale in N. 

Q6) Air contained within a verical piston cylinder assembly is shown in the figure below. On its top, the 10 kg piston is attached to a spring and exposed to an atmospheric pressure of 1 bar. Initially, the bottom of the piston is at x = 0, and the spring exerts a negligible force on the piston. The valve is opened and air enters the cylinder from the supply line, causing the volume of air within the cylinder to increase by 3.9 x 10-4 m3. The force exerted by the spring as the air expands within the cylinder varies linearly with x according to , where k = 10000 N/m. The piston face area is 7.8 x 10-3 m2. ignoring friction between the piston and cylinder walls, determine the pressure of air within the cylinder. 

Q7) Water, initially a saturated liquid at 100oC, is contained in a piston-cylinder assembly. The water undergoes a process to the corresponding saturated vapor state, during which the piston moves freely in the cylinder. If the change of state brought about by heating the water as it undergoes an internally reversible process at constant pressure and temperature, determine the work and heat transfer per unit mass, each in kJ/kg.

Q8) A 0.3 kg metal bar initially at 1200 K is removed from an oven and quenched by immersing it in a closed tank containing 9 kg of water initially at 300 K. Each substance can be modeled as incompressible. An appropriate constant specific heat value for metal is 0.42 kJ/kg K. Heat transfer from the tank contents can be neglected. Determine:

  1. the final equilibrium temperature of the metal bar and the water, in K
  2. the amount of entropy produced in kJ/K

Comments

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Mechanical Engineer by education, Entrepreneur by heart. Day by day nothing is changing but when we look behind, everything is different.

Sol for Q7

Work per unit mass = 2257 kJ/kg = heat transfer per unit mass

 

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Mechanical Engineer by education, Entrepreneur by heart. Day by day nothing is changing but when we look behind, everything is different.

Sol for Q8.

The final temperature is 303 K and entropy generation is 0.2027 kJ/K

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Mechanical Engineer by education, Entrepreneur by heart. Day by day nothing is changing but when we look behind, everything is different.

Sol to Q6. 

Initially x = 0 and there is no spring force acting on the piston. Also, friction between the piston and the cylinder wall can be ignored. Accordingly, the force exerted by the air withing the cylinder on the bottom of the piston is equal to the weight of the piston plus the force exerted by the atmposphere on the top of the piston. 

Finally, the force exerted by the air withing the cylinder on the bottom of the piston is equal to the weight of the piston plus the force exerted by the atmosphere on the top of the piston plus the force exerted by the spring on the top of the piston. 

So, 

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Mechanical Engineer by education, Entrepreneur by heart. Day by day nothing is changing but when we look behind, everything is different.

Q2 has been solved correctly by everyone. Find the soln from my end below. 

Constant C can be found out by applying PV = C, so  

Find 

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Mechanical Engineer by education, Entrepreneur by heart. Day by day nothing is changing but when we look behind, everything is different.

@Sagar Koneti nice work on Q1. There will be a minor difference in the final answer based on the steam tables. but this is acceptable.

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debanjan maity

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debanjan maity

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debanjan maity

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debanjan maity

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