Molecular Physics | Thermodynamics Answers

Umar has two pans, each containing 500cm3 of water. Pan 1 is made from copper and pan 2 is made from iron. Both have a mass of 1.5kg. Which pan will require more energy to heat the water to 100°C?

What is the thermal efficiency of an air standard gas turbine in %, if the density of the gas increases 345 % during compression and the heat capacity ratio is 1.39?

A capacitor is in series with a resistor and is charged to a potential of 100 V. When discharging the capacitor it takes 1.2 s for the potential across the capacitor to drop to 67 V. How long does it take the potential difference across the capacitor to drop to 30 V? (to 2 s.f and in s)

The maximum rate at which high performance athletes can do work is often limited by the rate at which they can get rid of heat from their body.


Assume that it is a warm day and an athletes only means of getting rid of body heat is the evaporation of sweat (water) from their skin. Assume the certain athlete does mechanical work with an efficiency of 15% and is capable of rehydrating at a rate of 1.5 litres of water per hour.


How much work can this athlete can do in one hour without dehydrating and while maintaining a constant body temperature? (to 2 s.f and in MJ)


[Lvap-water = 2560×103 J kg−1 at body temperature, for water 1 litre = 1 kg, assume all sweat evaporates]

You are breathing at a rate of 20 breaths per minute in a warm, dry environment.


Each time you take a breath, you breathe in 0.5×10−3 kg of air at a temperature of 24°C and with a relative humidity of 20%. You breathe out the same mass of air but at a temperature of 36°C and a relative humidity of 100%.


How much water vapour do you exhale in one hour under these circumstances? (to 2 s.f and in g)

A capacitor is in series with a resistor and is charged to a potential of 100 V. When discharging the capacitor it takes 1.2 s for the potential across the capacitor to drop to 67 V. How long does it take the potential difference across the capacitor to drop to 30 V? (to 2 s.f and in s)

Define a constant pressure process and draw the P-V diagram for a constant pressure process 2.025k of fluid at a pressure of 3bar with a specific internal energy and specific volume of 2544kj/kg and 0.6057m³/kg respectively is heated at constant pressure until the specific internal energy is 2807kj/kg and volume is 0.2189m³. Calculate the work done and heat supplied? Hint:V²=V²/m.

In an air motor cylinder the compressed air has an internal energyof 450kg/kj at the beginning of the expansion and an internal energy of 220kg/kj after expansion. If the work done by air during the expansion is 120kg/kj,calculate the heat flow to and fro the cylinder and state if the system gain or losses heat

A steel cube has sides of length 20cm. Calculate its mass. (Density of steel = 7.7

g/cm 3 ). Give your answer in g, and in kg.

A particle vector is given by r=2ti+t^2j. Find: (a) r at t=1 and t=3, respectively;

(b) the displacement of particle from t=1 to t= 3.

(c) the path equation of the particle