UA-78309841-1
Menu

Physicshelpline

Solution Search

Comments

. : "Heat and Thermodynamics"

Thermodynamics: Refrigerator

Q- A household refrigerator that has a power input of 450W and a COP of 2.5 is to cool 5 large watermelons, 10 kg each, to 10oC. If the melons are initially at 20oC, determine how long it will take for the refrigerator to cool them. The specific heat of melons = 4.2 kJ/(kg.oC)

Solution:

Read more

Heat and Thermodynamics

Q- A piston-cylinder device contains N2 gas, initially at 1.5 bar, 200C, 0.05 m3. The gas is now compressed in a polytropic process, PVn = constant, to 4 bar, 1500C. Determine the polytropic exponent ‘n’, the work done on the gas and the heat transfer.

Solution:

Read more

Thermodynamics

Q- 15 kg of air in a piston cylinder device is heated inside the cylinder from 250C to 750C by passing current through a resistance heater inside the cylinder. The pressure inside the cylinder is kept constant at 2 bar during the process and the heat loss of 50 kJ occurs. Determine the electrical en…

Read more

Thermal Radiation

Q- At high noon, the sun delivers 1000 W to each square meter of a blacktop road. If the hot asphalt loses energy only by radiation, what is its steady-state temperature?

Solution:

Read more

Heat Radiation

Q- A student is trying to decide what to wear. His bedroom is at 20.0 degrees Celsius. His skin temperature is 35.0 degrees Celsius. The area of his exposed skin is 1.50 m2. People all over the world have skin that is dark in the infrared, with emissivity about 0.900. Find the net energy loss from h…

Read more

Thermal Physics

Q- Work is done on the water by a rotating paddle wheel, which is driven by two blocks falling at a constant speed. The temperature of the stirred water increases due to friction between the water and the paddles. If the energy lost in the bearings and through the walls is neglected, then the loss i…

Read more

Thermodynamics

Q - Refrigerant R22 enters a well-insulated compressor at 3.5 bar, -50C and exits at 14 bar. Determine the work input in kJ/kg if the outlet temperature 750C. (γ = Cp/Cv for R22 is 1.562 at -50C and 1.348 at 750C)

Solution:

Read more

Heat and Thermodynamics

Q- A spherical tank contains 1 mole of helium gas at 10 bar and 300 K. The gas is slowly released to the atmosphere in such a way the remaining gas is maintained at constant total energy U. Heating or cooling may be used to keep U constant during the venting. Helium behaves as an ideal gas with a co…

Read more

Conduction Of Heat

Q- A glass windowpane has an area of 3.00 m2 and a thickness of 0.600 cm. If the temperature difference between its faces is 25.0 degrees Celsius, what is the rate of energy transfer by conduction through the window? (coefficient of conductivity for glass to be taken as 0.8 W/(m.K)

Solution:

Read more

Radiation: Stefan Law

Q- The surface of the sun has a temperature of about 5800K. The radius of the Sun is 6.96 X 108 m. Calculate the total energy radiated by the sun each second. Assume the emissivity is 0.986.

Solution:

Read more

Gas Laws

Q- At some place the temperature of air is 20 degrees C and the pressure is 1.021*105 Pa. Calculate the density of air.

Solution:

Read more

Thermal Physics: Latent Heat

Q- A 3.00-g lead bullet at 30.0 degrees C is fired at a speed of 240 m/s into a large block of ice at 0 degrees C, in which it embeds itself. What quantity of ice melts? (Specific heat capacity of lead is 128 J/kg/0C and latent heat of melting of ice is 333*103 J/kg)

Solution: 

Read more

Thermodynamics

Q- The initial state of 1.00 mol of a gas is P1 = 6.00 atm, V1 = 5.00 L, and Eint 1 = 790 J, The gas is allowed to expand at constant pressure to a volume of 9.00 L. It is then cooled at constant volume until its pressure is 4.00 atm and its final state becomes P2 = 4.00 atm, V2 = 9.00 L, and Eint 2

Read more

Thermal physics

Q-(a) If the pressure of a gas is increased by a factor of 9, while its volume is held constant, by what factor does rms speed change?(b) In Joule’s experiment, the mass of the weights is 2.99 kg, and the insulated tank is filled with 0.137 g of water. What is the increase in the temperature of the …

Read more

Thermal Physics: Boyle's Law

Q- A scuba diver releases a 2.50 cm diameter (spherical) bubble of air from a depth of 15 m in a lake. Assume the temperature is constant at 16.0C, and the air behaves as a perfect gas. What is the diameter of the bubble when it reaches the surface?

Solution:

Read more

Heat Engine

(On request Dyllzey)

Q- A gas is taken through the cycle as shown in the figure. Find

(a) Change in internal energy of the gas during one cycle  

(b) Work done on the gas during one cycle

(c) Net heat transferred to the gas during one cycle

Solution:

Read more

Thermal Physics: Gas Law

Q- A cylinder of hydrogen, 2m in height and with a 25cm diameter, is dropped and develops a crack of size 0.1 mm2. The gas is stored at 10 bar absolute pressure. Estimate how long it takes for half the contents to leak out. Explain your reasoning and assumptions.

Solution:

Read more

Thermal Radiations

Q- The radius of the Sun is 6.96 x 108 m and the total power output from its surface is 2.51 x 1026 W.
(a) Assuming that the Sun acts like a black body, calculate its surface temperature.
(b) What is the maximum wavelength of radiation from the Sun?

Solution:

Read more

Heat Engine

Q- One mole of an ideal monatomic gas is used as the working substance in an engine. The engine operates on the cycle shown in the diagram. Processes BC and DA are reversible and adiabatic. What is the efficiency of the engine?

Solution:

Read more

19 .