Molecular Physics | Thermodynamics Answers

A ball initially at rest rolls down a hill with an acceleration of 4.5 m/s^2
If it accelerates for 9 seconds, how far will it move?

A force vector has a magnit
ude of 575 newtons and points at
an angle of 36.0°
below the positive x axis. What
are (a) the x scalar component
and (b) the y scalar
component of the vector?

Specific heat capacity of water = 4200 J/kg/K
Specific heat capacity of aluminium = 900 J/kg/°C
Specific heat capacity of ice = 2100 J/ kg/K
Latent heat of fusion of ice = 334 000 J/ kg
Latent heat of vaporization of water =
2 250 000J/kg

We wish to determine the specific heat capacity of a new alloy of an unknown specific heat capacity.

A 0.15 kg sample of alloy is heated to 540°C. It is then quickly placed in 400 g of water at l0°C which is contained in a 200 g aluminium cup. The final temperature of the mixture is 305°C. Calculate the specific heat capacity of the alloy.

NB: Heat lost by alloy is gained by both the water and the cup containing the water.

A room in a house has a floor made entirely of concrete which is 200 mm thick. The lower surface of the concrete in contact with the ground has a temperature of 10°C and the upper surface, in contact with the living area has a temperature of 15°C. The floor is square and has sides 10m x 10m

a) Calculate the rate at which thermal energy ia conducted through the concrete. Assume the thermal conductivity of concrete is 0.750W/mK.

b) The temperature of thr carpet/concrete interface. The rate of conduction for both conductors are the same and the thermal conductivity of the carpet is 0.06W/mk.

c) The rate at which thermal energy is conducted through the two layers.

The following data was obtained during a test on a gaseous fuel using a Boys’ gas-type calorimeter. Gas supply pressure 20 mm H2O ,Gas supply temperature °C ,Volume of gas burned 0.010 m3 ,Exhaust gas temperature 19 °C ,Atmospheric pressure 99.5 kPa ,Cooling water inlet temperature 15 °C ,Cooling water outlet temperature 38 °C ,Mass of cooling water collected 2.55 kg ,Mass of condensate collected 5.15 g ,Determine the gross and net calorific values of the fuel measured in MJ m−3 at a normal temperature and pressure of 15 °C and 101.325 kPa, respectively. The specific heat capacity of water is 4187 J kg−1 K−1 and its specific latent heat of vaporisation is 2453 kJ kg−1.

A coal sample consists of 82.1% carbon, 4.5% hydrogen, 1.5% sulphur, 3.0% oxygen and the remainder incombustible material. If 1 kg is burnt with 20% excess air, determine (i) the mass of air required per kilogram of fuel and (ii) prepare an analysis by mass of the products of combustion per kilogram of fuel.

An oil- fired boiler takes in feed water at 75°C and produces wet steam at a pressure of 5 bars. The steam flow rate 1.50 tons/hr with a dryness fraction of 0.89. The fuel consumption rate is 6.10kg/min and its net calorific value is 41MJ/Kg. Determine the thermal efficiency of the boiler.

A sample of wet steam is passed through a simple throttling calorimeter. The steam entry pressure recorded on a gauge is 9 bar. Immediately after throttling, the temperature is 110 °C, where the steam is at atmospheric pressure of 1 bar. Calculate the dryness fraction of the steam sample.

Consider the Isentropic expansion of air from fixed, given reservoir conditions (i.e. total pressure and temperature). Investigate the behaviour of the value of the Reynolds number of the flow Re=(rho*U*L)/mu (based on a fixed reference length L), as a function of the Mach number M of the expanded flow.


For small values of M the thermodynamic properties of the flow will not deviate significantly from the reservoir conditions, hence Re increases linearly with U and therefore with M.

Show that for increasing expansion (i.e. increasing M) the value of Re will eventually decrease by investigating the limit behaviour for M>>1. For the temperature dependence of viscosity, employ, Sutherlands expression and the power law where w=1.5 - T_0/(T_0+S).

T_0=288K
S=111 K

A coal sample consists of 82.1% carbon, 4.5% hydrogen, 1.5% sulphur, 3.0% oxygen and the remainder incombustible material. If 1 kg is burnt with 20% excess air, determine (i) the mass of air required per kilogram of fuel and (ii) prepare an analysis by mass of the products of combustion per kilogram of fuel.