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mechanical engineering

Questions and Answers of Mechanical Engineering

Consider a mass going through a polytropic process where pressure is directly proportional to volume (n = − 1). The process start with P = 0, V = 0 and ends with P = 600 kPa, V = 0.01 m3. The
The piston/cylinder shown in Fig P4.48 contains carbon dioxide at 300 kPa, 100°C with a volume of 0.2 m3. Mass is added at such a rate that the gas compresses according to the relation PV1.2 =
A gas initially at 1 MPa, 500°C is contained in a piston and cylinder arrangement with an initial volume of 0.1 m3. The gas is then slowly expanded according to the relation PV = constant until a
Helium gas expands from 125 kPa, 350 K and 0.25 m3 to 100 kPa in a polytropic process with n = 1.667. How much work does it give out?
Air goes through a polytropic process from 125 kPa, 325 K to 300 kPa and 500 K. Find the polytropic exponent n and the specific work in the process.
A piston cylinder contains 0.1 kg air at 100 kPa, 400 K which goes through a polytropic compression process with n = 1.3 to a pressure of 300 kPa. How much work has the air done in the process?
A balloon behaves so the pressure is P = C2 V1/3, C2 = 100 kPa/m. The balloon is blown up with air from a starting volume of 1 m3 to a volume of 3 m3. Find the final mass of air assuming it is at
A balloon behaves such that the pressure inside is proportional to the diameter squared. It contains 2 kg of ammonia at 0°C, 60% quality. The balloon and ammonia are now heated so that a final
Consider a piston cylinder with 0.5 kg of R-134a as saturated vapor at -10°C. It is now compressed to a pressure of 500 kPa in a polytropic process with n = 1.5. Find the final volume and
Consider the process described in Problem 3.98. With 1 kg water as a control mass, determine the boundary work during the process. A spring-loaded piston/cylinder contains water at 500°C, 3 MPa.
Refrigerant-12 in a piston/cylinder arrangement is initially at 50°C, x = 1. It is then expanded in a process so that P = Cv−1 to a pressure of 100 kPa. Find the final temperature and specific
A piston/cylinder contains water at 500°C, 3 MPa. It is cooled in a polytropic process to 200°C, 1 MPa. Find the polytropic exponent and the specific work in the process.
Consider a two-part process with an expansion from 0.1 to 0.2 m3 at a constant pressure of 150 kPa followed by an expansion from 0.2 to 0.4 m3 with a linearly rising pressure from 150 kPa ending at
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
A piston/cylinder arrangement shown in Fig P4.61 initially contains air at 150 kPa, 400°C. The setup is allowed to cool to the ambient temperature of 20°C. a. Is the piston resting on the stops in
A piston cylinder has 1.5 kg of air at 300 K and 150 kPa. It is now heated up in a two step process. First constant volume to 1000 K (state 2) then followed by a constant pressure process to 1500 K,
A piston/cylinder assembly (Fig. P4.63) has 1 kg of R-134a at state 1 with 110°C, 600 kPa, and is then brought to saturated vapor, state 2, by cooling while the piston is locked with a pin. Now the
The refrigerant R-22 is contained in a piston/cylinder as shown in Fig. P4.64, where the volume is 11 L when the piston hits the stops the initial state is −30°C, 150 kPa with a volume of 10
A piston/cylinder contains 50 kg of water at 200 kPa with a volume of 0.1 m3. A stop in the cylinder restricts the enclosed volume to 0.5 m3, similar to the setup in Problem 4.7. The water is now
Ammonia in a piston/cylinder arrangement is at 700 kPa, 80°C. It is now cooled at constant pressure to saturated vapor (state 2) at which point the piston is locked with a pin. The cooling continues
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
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
Ammonia at 10oC with a mass of 10 kg is in a piston cylinder arrangement with an initial volume of 1 m3. The piston initially resting on the stops has a mass such that a pressure of 900 kPa will
A piston cylinder setup similar to Problem 4.68 contains 0.1 kg saturated liquid and vapor water at 100 kPa with quality 25%. The mass of the piston is such that a pressure of 500 kPa will float it.
A 0.5-m-long steel rod with a 1-cm diameter is stretched in a tensile test. What is the required work to obtain a relative strain of 0.1%? The modulus of elasticity of steel is 2 × 108 kPa.
A copper wire of diameter 2 mm is 10 m long and stretched out between two posts. The normal stress (pressure) σ = E (L – Lo)/Lo, depends on the length L versus the unstretched length Lo and
A film of ethanol at 20°C has a surface tension of 22.3 mN/m and is maintained on a wire frame as shown in Fig. P4.73. Consider the film with two surfaces as a control mass and find the work done
Assume a balloon material with a constant surface tension of S = 2 N/m. What is the work required to stretch a spherical balloon up to a radius of r = 0.5 m? Neglect any effect from atmospheric
A soap bubble has a surface tension of S = 3 × 10-4 N/cm as it sits flat on a rigid ring of diameter 5 cm. You now blow on the film to create a half sphere surface of diameter 5 cm. How much work
Assume we fill a spherical balloon from a bottle of helium gas. The helium gas provides work ∫ PdV that stretches the balloon material ∫ S dA and pushes back the atmosphere ∫ Po dV.
A sheet of rubber is stretched out over a ring of radius 0.25 m. I pour liquid water at 20oC on it so the rubber forms a half sphere (cup). Neglect the rubber mass and find the surface tension near
Consider a window-mounted air conditioning unit used in the summer to cool incoming air. Examine the system boundaries for rates of work and heat transfer, including signs.
Consider a hot-air heating system for a home. Examine the following systems for heat transfer. a) The combustion chamber and combustion gas side of the heat transfer area. b) The furnace as a
Consider a household refrigerator that has just been filled up with room-temperature food. Define a control volume (mass) and examine its boundaries for rates of work and heat transfer, including
A room is heated with an electric space heater on a winter day. Examine the following control volumes, regarding heat transfer and work, including sign. a) The space heater. b) Room c) The space
An escalator raises a 100 kg bucket of sand 10 m in 1 minute. Determine the rate of work done during the process.
A car uses 25 hp to drive at a horizontal level at constant 100 km/h. What is the traction force between the tires and the road?
A piston/cylinder of cross sectional area 0.01 m2 maintains constant pressure. It contains 1 kg water with a quality of 5% at 150oC. If we heat so 1 g/s liquid turns into vapor what is the rate of
A crane lifts a bucket of cement with a total mass of 450 kg vertically up with a constant velocity of 2 m/s. Find the rate of work needed to do that.
Helium gas expands from 20 psia, 600 R and 9 ft3 to 15 psia in a polytropic process with n = 1.667. How much work does it give out?
Consider the car with the rolling resistance as in problem 4.27. How fast can it drive using 30 hp?
Consider the car with the air drag force as in problem 4.29. How fast can it drive using 30 hp?
Consider a 1400 kg car having the rolling resistance as in problem 4.27 and air resistance as in problem 4.29. How fast can it drive using 30 hp?
A battery is well insulated while being charged by 12.3 V at a current of 6 A. Take the battery as a control mass and compute the instantaneous rate of work and the total work done over 4 hours.
A current of 10 amp runs through a resistor with a resistance of 15 ohms. Find the rate of work that heats the resistor up.
A pressure of 650 kPa pushes a piston of diameter 0.25 m with V = 5 m/s. What is the volume displacement rate, the force and the transmitted power?
Assume the process in Problem 4.37 takes place with a constant rate of change in volume over 2 minutes. Show the power (rate of work) as a function of time.
Air at a constant pressure in a piston cylinder is at 300 kPa, 300 K and a volume of 0.1 m3. It is heated to 600 K over 30 seconds in a process with constant piston velocity. Find the power delivered
A torque of 650 Nm rotates a shaft of diameter 0.25 m with ω = 50 rad/s. What are the shaft surface speed and the transmitted power?
The sun shines on a 150 m2 road surface so it is at 45°C. Below the 5 cm thick asphalt, average conductivity of 0.06 W/m K, is a layer of compacted rubbles at a temperature of 15°C. Find the rate
A pot of steel, conductivity 50 W/m K, with a 5 mm thick bottom is filled with 15°C liquid water. The pot has a diameter of 20 cm and is now placed on an electric stove that delivers 250 W as heat
A water-heater is covered up with insulation boards over a total surface area of 3 m2. The inside board surface is at 75°C and the outside surface is at 20°C and the board material has a
You drive a car on a winter day with the atmospheric air at −15°C and you keep the outside front windshield surface temperature at +2°C by blowing hot air on the inside surface. If the
A large condenser (heat exchanger) in a power plant must transfer a total of 100 MW from steam running in a pipe to sea water being pumped through the heat exchanger. Assume the wall separating the
The black grille on the back of a refrigerator has a surface temperature of 35°C with a total surface area of 1 m2. Heat transfer to the room air at 20°C takes place with an average convective heat
Due to a faulty door contact the small light bulb (25 W) inside a refrigerator is kept on and limited insulation lets 50 W of energy from the outside seep into the refrigerated space. How much of a
The brake shoe and steel drum on a car continuously absorbs 25 W as the car slows down. Assume a total outside surface area of 0.1 m2 with a convective heat transfer coefficient of 10 W/m2 K to the
A wall surface on a house is at 30°C with an emissivity of ε = 0.7. The surrounding ambient to the house is at 15°C, average emissivity of 0.9. Find the rate of radiation energy from each of
A log of burning wood in the fireplace has a surface temperature of 450°C. Assume the emissivity is 1 (perfect black body) and find the radiant emission of energy per unit surface area.
A radiant heat lamp is a rod, 0.5 m long and 0.5 cm in diameter, through which 400 W of electric energy is deposited. Assume the surface has an emissivity of 0.9 and neglect incoming radiation. What
A vertical cylinder (Fig P4.106) has a 61.18-kg piston locked with a pin trapping 10 L of R-22 at 10°C, 90% quality inside. Atmospheric pressure is 100 kPa, and the cylinder cross-sectional area is
A piston/cylinder contains butane, C4H10, at 300°C, 100 kPa with a volume of 0.02 m3. The gas is now compressed slowly in an isothermal process to 300 kPa. a. Show that it is reasonable to assume
A cylinder fitted with a piston contains propane gas at 100 kPa, 300 K with a volume of 0.2 m3. The gas is now slowly compressed according to the relation PV1.1 = constant to a final temperature of
The gas space above the water in a closed storage tank contains nitrogen at 25°C, 100 kPa. Total tank volume is 4 m3, and there is 500 kg of water at 25°C. An additional 500 kg water is now forced
Two kilograms of water is contained in a piston/cylinder (Fig. P4.110) with a mass less piston loaded with a linear spring and the outside atmosphere, initially the spring force is zero and P1 = Po =
A cylinder having an initial volume of 3 m3 contains 0.1 kg of water at 40°C. The water is then compressed in an isothermal quasi-equilibrium process until it has a quality of 50%. Calculate the
Air at 200 kPa, 30°C is contained in a cylinder/piston arrangement with initial volume 0.1 m3. The inside pressure balances ambient pressure of 100 kPa plus an externally imposed force that is
A spring-loaded piston/cylinder arrangement contains R-134a at 20°C, 24% quality with a volume 50 L. The setup is heated and thus expands, moving the piston. It is noted that when the last drop of
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
Two springs with same spring constant are installed in a mass less piston/cylinder with the outside air at 100 kPa. If the piston is at the bottom, both springs are relaxed and the second spring
A piston/cylinder arrangement is loaded with a linear spring and the outside atmosphere. It contains water at 5 MPa, 400°C with the volume being 0.1 m3. If the piston is at the bottom, the spring
The electric company charges the customers per kW-hour. What is that in English units?
Work as F Δx has units of lbf-ft, what is that in Btu?
A work of 2.5 Btu must be delivered on a rod from a pneumatic piston/cylinder where the air pressure is limited to 75 psia. What diameter cylinder should I have to restrict the rod motion to maximum
A force of 300 lbf moves a truck with 40 mi/h up a hill. What is the power?
A 1200 hp dragster engine drives the car with a speed of 65 mi/h. How much force is between the tires and the road?
A 1200 hp dragster engine has a drive shaft rotating at 2000 RPM. How much torque is on the shaft?
A bulldozer pushes 1000 lbm of dirt 300 ft with a force of 400 lbf. It then lifts the dirt 10 ft up to put it in a dump truck. How much work did it do in each situation?
A steam radiator in a room at 75 F has saturated water vapor at 16 lbf/in.2 flowing through it when the inlet and exit valves are closed what is the pressure and the quality of the water, when it has
A linear spring, F = ks (x − xo), with spring constant ks = 35 lbf/ft, is stretched until it is 2.5 in. longer. Find the required force and work input.
Two hydraulic cylinders maintain a pressure of 175 psia. One has a cross sectional area of 0.1 ft2 the other 0.3 ft2. To deliver a work of 1 Btu to the piston how large a displacement (V) and piston
A piston/cylinder has 15 ft of liquid 70 F water on top of the piston (m = 0) with cross-sectional area of 1 ft2, see Fig. P2.57. Air is let in under the piston that rises and pushes the water out
A cylinder fitted with a frictionless piston contains 10 lbm of superheated refrigerant R-134a vapor at 100 lbf/in.2, 300 F the setup is cooled at constant pressure until the R-134a reaches a quality
The gas space above the water in a closed storage tank contains nitrogen at 80 F, 15 lbf/in.2 Total tank volume is 150 ft3 and there is 1000 lbm of water at 80 F. An additional 1000 lbm water is now
A cylinder having an initial volume of 100 ft3 contains 0.2 lbm of water at 100 F. The water is then compressed in an isothermal quasi-equilibrium process until it has a quality of 50%. Calculate the
Consider a mass going through a polytropic process where pressure is directly proportional to volume (n = − 1). The process start with P = 0, V = 0 and ends with P = 90 lbf/in.2, V = 0.4
The piston/cylinder shown in Fig P4.48 contains carbon dioxide at 50 lbf/in.2, 200 F with a volume of 5 ft3 Mass is added at such a rate that the gas compresses according to the relation PV1.2 =
Find the work for Problem 3.156E.
Consider a two-part process with an expansion from 3 to 6 ft3 at a constant pressure of 20 lbf/in.2 followed by an expansion from 6 to 12 ft3 with a linearly rising pressure from 20 lbf/in.2 ending
A piston/cylinder has 2 lbm of R-134a at state 1 with 200 F, 90 lbf/in 2 and is then brought to saturated vapor, state 2, by cooling while the piston is locked with a pin. Now the piston is balanced
A cylinder containing 2 lbm of ammonia has an externally loaded piston. Initially the ammonia is at 280 lbf/in 2 360 F and is now cooled to saturated vapor at 105 F, and then further cooled to 65 F,
A 1-ft-long steel rod with a 0.5-in. diameter is stretched in a tensile test. What is the required work to obtain a relative strain of 0.1%? The modulus of elasticity of steel is 30 × 106 lbf/in.2.
An escalator raises a 200 lbm bucket of sand 30 ft in 1 minute. Calculate the total amount of work done and the instantaneous rate of work during this process
A piston/cylinder of diameter 10 inches moves a piston with a velocity of 18 ft/s. The instantaneous pressure is 100 psia. What is the volume displacement rate, the force and the transmitted power?
The sun shines on a 1500 ft2 road surface so it is at 115 F. Below the 2 inch thick asphalt, average conductivity of 0.035 Btu/h ft F, is a layer of compacted rubbles at a temperature of 60 F. Find
A water-heater is covered up with insulation boards over a total surface area of 30 ft2. The inside board surface is at 175 F and the outside surface is at 70 F and the board material has a
The black grille on the back of a refrigerator has a surface temperature of 95 F with a total surface area of 10 ft2. Heat transfer to the room air at 70 F takes place with an average convective heat
What is 1 cal in SI units and what is the name given to 1 N-m?
In a complete cycle what is the net change in energy and in volume?
Why do we write ΔE or E2 – E1 whereas we write 1Q2 and 1W2?

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