Molecular Physics | Thermodynamics Answers

A small probe is made of stainless steel and has a length of 164.1 mm when being used to monitor the temperature in a furnace.
When the probe is removed for maintenance and allowed to cool to 20.0°C the length of the probe is measured as 162.2 mm.
What is the temperature of the furnace? (to 3 s.f and in °C)
[αsteel = 16.0×10−6 K−1]

You are jogging along at a slow speed on a cool day and are losing heat at a rate of 120 W via convection. If your surface area is 0.45 m2, your skin temperature is 26°C. and the air temperature is 17°C then what is the heat transfer coefficient of convection, hconv? (to 2 s.f and in W m−2 K−1)

While helping a friend shift furniture you do 2.2 MJ of mechanical work at and efficiency of 11% (η = 0.11).
How much food energy would you need to ingest in order to prevent weight loss? (to 2 s.f and in MJ)

A student is doing an experiment using a 200 W heat plate. He is heating a 300 g block of ice at -20°C to water at
20°C. How long will it take?

calculate steady state temperature of the black body copper disc of radius 4cm and mass 10g. at surrounding temperature of 50 C . when kept initially at 25 C.Also determine stefan boltzmann constant

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)