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engineering
mechanical engineering

Questions and Answers of Mechanical Engineering

When you wind a spring up in a toy or stretch a rubber band what happens in terms of work, energy and heat transfer? Later when they are released, what happens then?
Explain in words what happens with the energy terms for the stone in Example 5.2. What would happen if it were a bouncing ball falling to a hard surface?
Make a list of at least 5 systems that store energy, explaining which form of energy.
A 1200 kg car is accelerated from 30 to 50 km/h in 5 s. How much work is that? If you continue from 50 to 70 km/h in 5 s is that the same?
A crane use 2 kW to raise a 100 kg box 20 m. How much time does it take?
Saturated water vapor has a maximum for u and h at around 235oC. Is it similar for other substances?
A pot of water is boiling on a stove supplying 325 W to the water. What is the rate of mass (kg/s) vaporizing assuming a constant pressure process?
A constant mass goes through a process where 100 W of heat transfer comes in and 100 W of work leaves. Does the mass change state?
I have 2 kg of liquid water at 20oC, 100 kPa. I now add 20 kJ of energy at a constant pressure. How hot does it get if it is heated? How fast does it move if it is pushed by a constant horizontal
Water is heated from 100 kPa, 20oC to 1000 kPa, 200oC. In one case pressure is raised at T = C, then T is raised at P = C. In a second case the opposite order is done. Does that make a difference for
Two kg water at 120oC with a quality of 25% has its temperature raised 20oC in a constant volume process. What are the new quality and specific internal energy?
Two kg water at 200 kPa with a quality of 25% has its temperature raised 20oC in a constant pressure process. What is the change in enthalpy?
You heat a gas 10 K at P = C. Which one in table A.5 requires most energy? Why?
Air is heated from 300 to 350 K at V = C. Find 1q2? What if from 1300 to 1350 K?
A mass of 3 kg nitrogen gas at 2000 K, V = C, cools with 500 W. What is dT/dt?
A drag force on a car, with frontal area A = 2 m2, driving at 80 km/h in air at 20oC is Fd = 0.225 A ρairV2. How much power is needed and what is the traction force?
A hydraulic hoist raises a 1750 kg car 1.8 m in an auto repair shop. The hydraulic pump has a constant pressure of 800 kPa on its piston. What is the increase in potential energy of the car and how
A piston motion moves a 25 kg hammerhead vertically down 1 m from rest to a velocity of 50 m/s in a stamping machine. What is the change in total energy of the hammerhead?
Airplane takeoff from an aircraft carrier is assisted by a steam driven piston/cylinder device with an average pressure of 1250 kPa. A 17500 kg airplane should be accelerated from zero to a speed of
Solve Problem 5.22, but assume the steam pressure in the cylinder starts at 1000 kPa, dropping linearly with volume to reach 100 kPa at the end of the process.
A 1200 kg car accelerates from zero to 100 km/h over a distance of 400 m. The road at the end of the 400 m is at 10 m higher elevation. What is the total increase in the car kinetic and potential
A 25 kg piston is above a gas in a long vertical cylinder. Now the piston is released from rest and accelerates up in the cylinder reaching the end 5 m higher at a velocity of 25 m/s. The gas
The rolling resistance of a car depends on its weight as: F = 0.006 mg. How far will a car of 1200 kg roll if the gear is put in neutral when it drives at 90 km/h on a level road without air
A mass of 5 kg is tied to an elastic cord, 5 m long, and dropped from a tall bridge. Assume the cord, once straight, acts as a spring with k = 100 N/m. Find the velocity of the mass when the cord is
Find the missing properties. a. H2O T = 250°C, v = 0.02 m3/kg P = ? u = ? b. N2 T = 120 K, P = 0.8 MPa x = ? h = ? c. H2O T = −2°C, P = 100 kPa u = ? v = ? d. R-134a P = 200
Find the missing properties of T, P, v, u, h and x if applicable and plot the location of the three states as points in the T-v and the P-v diagrams a. Water at 5000 kPa, u = 800 kJ/kg b. Water at
Find the missing properties and give the phase of the ammonia, NH3. a. T = 65oC, P = 600 kPa u =? v =? b. T = 20oC, P = 100 kPa u =? v =? x =? c. T = 50oC, v = 0.1185 m3/kg u =? P =? x =?
Find the phase and missing properties of P, T, v, u, and x. a. Water at 5000 kPa, u = 1000 kJ/kg (Table B.1 reference) b. R-134a at 20oC, u = 300 kJ/kg c. Nitrogen at 250 K, 200 kPa Show also the
Find the missing properties and give the phase of the substance a. H2O T = 120°C, v = 0.5 m3/kg u =? P =? x =? b. H2O T = 100°C, P = 10 MPa u =? x =? v =? c. N2 T = 200 K, P = 200 kPa v
Find the missing properties among (T, P, v, u, h and x if applicable) and give the phase of the substance and indicate the states relative to the two-phase region in both a T-v and a P-v diagram. a.
Saturated liquid water at 20oC is compressed to a higher pressure with constant temperature. Find the changes in u and h from the initial state when the final pressure is a) 500 kPa, b) 2000 kPa,
A 100-L rigid tank contains nitrogen (N2) at 900 K, 3 MPa. The tank is now cooled to 100 K. What are the work and heat transfer for this process?
A rigid container has 0.75 kg water at 300oC, 1200 kPa. The water is now cooled to a final pressure of 300 kPa. Find the final temperature, the work and the heat transfer in the process.
A cylinder fitted with a frictionless piston contains 2 kg of superheated refrigerant R-134a vapor at 350 kPa, 100oC. The cylinder is now cooled so the R-134a remains at constant pressure until it
Ammonia at 0°C, quality 60% is contained in a rigid 200-L tank. The tank and ammonia is now heated to a final pressure of 1 MPa. Determine the heat transfer for the process.
Water in a 150-L closed, rigid tank is at 100°C, 90% quality. The tank is then cooled to −10°C. Calculate the heat transfer during the process.
A piston/cylinder contains 1 kg water at 20oC with volume 0.1 m3. By mistake someone locks the piston preventing it from moving while we heat the water to saturated vapor. Find the final temperature
A test cylinder with constant volume of 0.1 L contains water at the critical point. It now cools down to room temperature of 20°C. Calculate the heat transfer from the water.
A 10-L rigid tank contains R-22 at −10°C, 80% quality. A 10-A electric current (from a 6-V battery) is passed through a resistor inside the tank for 10 min, after which the R-22 temperature is
A piston/cylinder contains 50 kg of water
A constant pressure piston/cylinder assembly contains 0.2 kg water as saturated vapor at 400 kPa. It is now cooled so the water occupies half the original volume. Find the heat transfer in the
Two kg water at 120oC with a quality of 25% has its temperature raised 20oC in a constant volume process as in Fig. P5.45. What are the heat transfer and work in the process?
A 25 kg mass moves with 25 m/s. Now a brake system brings the mass to a complete stop with a constant deceleration over a period of 5 seconds. The brake energy is absorbed by 0.5 kg water initially
An insulated cylinder fitted with a piston contains R-12 at 25°C with a quality of 90% and a volume of 45 L. The piston is allowed to move, and the R-12 expands until it exists as saturated vapor.
A water-filled reactor with volume of 1 m3 is at 20 MPa, 360°C and placed inside a containment room as shown in Fig. P5.48. The room is well insulated and initially evacuated. Due to a failure, the
A piston/cylinder arrangement contains water of quality x = 0.7 in the initial volume of 0.1 m3, where the piston applies a constant pressure of 200 kPa. The system is now heated to a final
A piston/cylinder arrangement has the piston loaded with outside atmospheric pressure and the piston mass to a pressure of 150 kPa, shown in Fig. P5.50. It contains water at −2°C, which is
A piston/cylinder assembly contains 1 kg of liquid water at 20oC and 300 kPa. There is a linear spring mounted on the piston such that when the water is heated the pressure reaches 1 MPa with a
A closed steel bottle contains ammonia at −20°C, x = 20% and the volume is 0.05 m3. It has a safety valve that opens at a pressure of 1.4 MPa. By accident, the bottle is heated until the
Two kg water at 200 kPa with a quality of 25% has its temperature raised 20oC in a constant pressure process. What are the heat transfer and work in the process?
Two kilograms of nitrogen at 100 K, x = 0.5 is heated in a constant pressure process to 300 K in a piston/cylinder arrangement. Find the initial and final volumes and the total heat transfer required.
A 1-L capsule of water at 700 kPa, 150°C is placed in a larger insulated and otherwise evacuated vessel. The capsule breaks and its contents fill the entire volume. If the final pressure should not
Superheated refrigerant R-134a at 20°C, 0.5 MPa is cooled in a piston/cylinder arrangement at constant temperature to a final two-phase state with quality of 50%. The refrigerant mass is 5 kg, and
A cylinder having a piston restrained by a linear spring (of spring constant 15 kN/m) contains 0.5 kg of saturated vapor water at 120°C, as shown in Fig. P5.57. Heat is transferred to the water,
A rigid tank is divided into two rooms by a membrane, both containing water, shown in Fig. P5.58. Room A is at 200 kPa, v = 0.5 m3/kg, VA = 1 m3, and room B contains 3.5 kg at 0.5 MPa, 400°C. The
A 10-m high open cylinder, Acyl = 0.1 m2, contains 20°C water above and 2 kg of 20°C water below a 198.5-kg thin insulated floating piston, shown in Fig. P5.59. Assume standard g, Po Now heat is
Assume the same setup as in Problem 5.48, but the room has a volume of 100 m3. Show that the final state is two-phase and find the final pressure by trial and error.
10 kg of water in a piston cylinder arrangement exists as saturated liquid/vapor at 100 kPa, with a quality of 50%. It is now heated so the volume triples. The mass of the piston is such that a
Two tanks are connected by a valve and line as shown in Fig. P5.62. The volumes are both 1 m3 with R-134a at 20°C, quality 15% in A and tank B is evacuated. The valve is opened and saturated vapor
Consider the same system as in the previous problem. Let the valve be opened and transfer enough heat to both tanks so all the liquid disappears. Find the necessary heat transfer.
A vertical cylinder fitted with a piston contains 5 kg of R-22 at 10°C. Heat is transferred to the system, causing the piston to rise until it reaches a set of stops at which point the volume has
A piston/cylinder contains 1 kg of liquid water at 20°C and 300 kPa. Initially the piston floats, similar to the setup in Problem 4.64, with a maximum enclosed volume of 0.002 m3 if the piston
Refrigerant-12 is contained in a piston/cylinder arrangement at 2 MPa, 150°C with a mass less piston against the stops, at which point V = 0.5 m3. The side above the piston is connected by an open
A piston/cylinder (Fig P4.114) contains 1 kg of water at 20°C with a volume of 0.1 m3. Initially the piston rests on some stops with the top surface open to the atmosphere, Po and a mass so a water
A rigid container has two rooms filled with water, each 1 m3 separated by a wall. Room A has P = 200 kPa with a quality x = 0.80. Room B has P = 2 MPa and T = 400°C. The partition wall is removed
The cylinder volume below the constant loaded piston has two compartments A and B filled with water. A has 0.5 kg at 200 kPa, 150oC and B has 400 kPa with a quality of 50% and a volume of 0.1 m3. The
A rigid tank A of volume 0.6 m3 contains 3 kg water at 120oC and the rigid tank B is 0.4 m3 with water at 600 kPa, 200oC. They are connected to a piston cylinder initially empty with closed valves.
A cylinder containing 1 kg of ammonia has an externally loaded piston. Initially the ammonia is at 2 MPa, 180°C and is now cooled to saturated vapor at 40°C, and then further cooled to 20°C, at
Calculate the heat transfer for the process described in Problem 4.70. A piston cylinder setup similar to Problem 4.24 contains 0.1 kg saturated liquid and vapor water at 100 kPa with quality 25%.
A cylinder/piston arrangement contains 5 kg of water at 100°C with x = 20% and the piston, mP = 75 kg, resting on some stops, similar to Fig. P5.73. The outside pressure is 100 kPa, and the cylinder
Because a hot water supply must also heat some pipe mass as it is turned on so it does not come out hot right away. Assume 80oC liquid water at 100 kPa is cooled to 45oC as it heats 15 kg of copper
A house is being designed to use a thick concrete floor mass as thermal storage material for solar energy heating. The concrete is 30 cm thick and the area exposed to the sun during the daytime is 4
A copper block of volume 1 L is heat treated at 500°C and now cooled in a 200-L oil bath initially at 20°C, shown in Fig. P5.76. Assuming no heat transfer with the surroundings, what is the final
A 1 kg steel pot contains 1 kg liquid water both at 15oC. It is now put on the stove where it is heated to the boiling point of the water. Neglect any air being heated and find the total amount of
A car with mass 1275 kg drives at 60 km/h when the brakes are applied quickly to decrease its speed to 20 km/h. Assume the brake pads are 0.5 kg mass with heat capacity of 1.1 kJ/kg K and the brake
Saturated, x=1%, water at 25°C is contained in a hollow spherical aluminum vessel with inside diameter of 0.5 m and a 1-cm thick wall. The vessel is heated until the water inside is saturated vapor.
A 25 kg steel tank initially at –10oC is filled up with 100 kg of milk (assume properties as water) at 30oC. The milk and the steel come to a uniform temperature of +5 oC in a storage room. How
An engine consists of a 100 kg cast iron block with a 20 kg aluminum head, 20 kg steel parts, 5 kg engine oil and 6 kg glycerine (antifreeze). Everything begins at 5oC and as the engine starts we
Use the ideal gas air table A.7 to evaluate the heat capacity Cp at 300 K as a slope of the curve h(T) by Δh/ΔT. How much larger is it at 1000 K and 1500 K.
We want to find the change in u for carbon dioxide between 600 K and 1200 K. a) Find it from a constant Cvo from table A.5 b) Find it from a Cvo evaluated from equation in A.6 at the average T. c)
We want to find the change in u for oxygen gas between 600 K and 1200 K. a) Find it from a constant Cvo from table A.5 b) Find it from a Cvo evaluated from equation in A.6 at the average T. c)
Water at 20°C, 100 kPa, is brought to 200 kPa, 1500°C. Find the change in the specific internal energy, using the water table and the ideal gas water table in combination.
We want to find the increase in temperature of nitrogen gas at 1200 K when the specific internal energy is increased with 40 kJ/kg a) Find it from a constant Cvo from table A.5 b) Find it from a
For an application the change in enthalpy of carbon dioxide from 30 to 1500°C at 100 kPa is needed. Consider the following methods and indicate the most accurate one. a. Constant specific heat,
An ideal gas is heated from 500 to 1500 K. Find the change in enthalpy using constant specific heat from Table A.5 (room temperature value) and discuss the accuracy of the result if the gas is a.
A 250 L rigid tank contains methane at 500 K, 1500 kPa. It is now cooled down to 300 K. Find the mass of methane and the heat transfer using a) ideal gas and b) the methane tables.
A rigid insulated tank is separated into two rooms by a stiff plate. Room A of 0.5 m3 contains air at 250 kPa, 300 K and room B of 1 m3 has air at 150 kPa, 1000 K. The plate is removed and the air
A rigid container has 2 kg of carbon dioxide gas at 100 kPa, 1200 K that is heated to 1400 K. Solve for the heat transfer using a. the heat capacity from Table A.5 and b. properties from Table A.8
Do the previous problem for nitrogen, N2, gas. A rigid container has 2 kg of carbon dioxide gas at 100 kPa, 1200 K that is heated to 1400 K. Solve for the heat transfer using a. the heat capacity
A 10-m high cylinder, cross-sectional area 0.1 m2, has a mass less piston at the bottom with water at 20°C on top of it, shown in Fig. P5.93. Air at 300 K, volume 0.3 m3, under the piston is heated
A piston cylinder contains 3 kg of air at 20oC and 300 kPa. It is now heated up in a constant pressure process to 600 K.
An insulated cylinder is divided into two parts of 1 m3 each by an initially locked piston. Side A has air at 200 kPa, 300 K, and side B has air at 1.0 MPa, 1000 K. The piston is now unlocked so it
A piston cylinder contains air at 600 kPa, 290 K and a volume of 0.01 m3. A constant pressure process gives 54 kJ of work out. Find the final temperature of the air and the heat transfer input.
A cylinder with a piston restrained by a linear spring contains 2 kg of carbon dioxide at 500 kPa, 400°C. It is cooled to 40°C, at which point the pressure is 300 kPa. Calculate the heat transfer
Water at 100 kPa, 400 K is heated electrically adding 700 kJ/kg in a constant pressure process? Find the final temperature using a) The water tables B.1 b) The ideal gas tables A.8 c) Constant
A piston/cylinder has 0.5 kg air at 2000 kPa, 1000 K as shown. The cylinder has stops so Vmin = 0.03 m3. The air now cools to 400 K by heat transfer to the ambient. Find the final volume and pressure
A spring loaded piston/cylinder contains 1.5 kg of air at 27C and 160 kPa. It is now heated to 900 K in a process where the pressure is linear in volume to a final volume of twice the initial volume.
Air in a piston/cylinder at 200 kPa, 600 K, is expanded in a constant-pressure process to twice the initial volume (state 2), shown in Fig. P5.101. The piston is then locked with a pin and heat is
A vertical piston/cylinder has a linear spring mounted as shown so at zero cylinder volume a balancing pressure inside is zero. The cylinder contains 0.25 kg air at 500 kPa, 27oC. Heat is now added
A piston cylinder contains 0.1 kg air at 300 K and 100 kPa. The air is now slowly compressed in an isothermal (T = C) process to a final pressure of 250 kPa. Show the process in a P-V diagram and

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