Exam 20: The First Law of Thermodynamics

If a person in Alaska were locked out of his house on a day when the temperature outside was −40°C,his thick clothing would mostly reduce the loss of thermal energy by

A 100 kg marble slab falls off a skyscraper and falls 200 m to the ground without hitting anyone.Its fall stops within milliseconds,so that there is no loss of thermal energy to its surroundings if its temperature is measured immediately after it stops.By how much has its temperature changed as a result of the fall,if we ignore energy gained or lost as a result of its interaction with the atmosphere? ( ) )

100 grams of liquid nitrogen at 77 K is stirred into a beaker containing 200 grams of 5°C water.If the nitrogen leaves the solution as soon as it turns to gas,how much water freezes? (The heat of evaporation of nitrogen is 6.09 cal/gram and the heat of fusion of water is 80 cal/gram. )

We are able to define a mechanical equivalent for heat because

Aluminum rod #1 is 1.0 m long with cross-section area 2.0 cm².Aluminum rod #2 is 2.0 m long with cross-section area 4.0 cm².Aluminum rod #3 is 3.0 m long with cross-section area 9.0 cm².If each rod has the same temperature difference applied across its ends,which rod has the greatest rate of transfer of energy between its ends?

An 8 000-kg aluminum flagpole 100-m long is heated by the sun from a temperature of 10°C to 20°C.Find the heat transferred (in J)to the aluminum if the specific heat of aluminum is 0.215 cal/g⋅°C.

A super-insulated house is at a temperature of 20°C.The temperature outside is 0°C.The surface area of the house is 200 m²,and the emissivity is 1.Approximately how much energy is radiated (in W)per second?

Which statement below regarding the First Law of Thermodynamics is most correct?

Star A has a radius of 200 000 km and a surface temperature of 6 000 K.Star B has a radius of 400 000 km and a surface temperature of 3 000 K.The emissivity of both stars is the same.What is the ratio of the rate of energy radiated by Star A to that of Star B?

A team of people who traveled to the North Pole by dogsled lived on butter because they needed to consume 6 000 dietician's Calories each day.Because the ice there is lumpy and irregular,they had to help the dogs by pushing and lifting the load.Assume they had a 16 hour working day and that each person could lift a 500 N load.How many times would a person have to lift this weight 1.00 m upwards in a constant gravitational field where To do the work equivalent to 6 000 Calories?

The work done in the expansion from an initial to a final state

Duff states that equal masses of all substances have equal changes in internal energy when they have equal changes in temperature.Javan states that the change in internal energy is equal to a constant times the change in temperature for every ΔT,no matter how large or how small ΔT is,but that the constant is different for different substances.Which one,if either,is correct?

An 8 000-kg aluminum flagpole 100-m high is heated by the sun from a temperature of 10°C to 20°C.Find the increase in internal energy (in J)of the aluminum.(The coefficient of linear expansion is 24 × 10−⁶ (°C)−¹,the density is 2.7 × 10³ kg/m³,and the specific heat of aluminum is 0.215 cal/g⋅°C. )

A 100-kg student eats a 200-Calorie doughnut.To "burn it off",he decides to climb the steps of a tall building.How high (in m)would he have to climb to expend an equivalent amount of work? (1 food Calorie = 10³ calories. )

Two kilograms of water at 100°C is converted to steam at 1 atm.Find the work done (in J).(The density of steam at 100°C is 0.598 kg/m³. )

In an isobaric process

A 300-g glass thermometer initially at 25°C is put into 200 cm³ of hot water at 95°C.Find the final temperature (in °C)of the thermometer,assuming no heat flows to the surroundings.(The specific heat of glass is 0.2 cal/g⋅°C. )

A slab of concrete and an insulating board are in thermal contact with each other.The temperatures of their outer surfaces are 68°F and 50°F.Determine the rate of heat transfer (in BTU/ft²⋅h)if the R values are 1.93 and 8.7 ft²⋅°F⋅h/BTU,respectively.

One gram of water is heated from 0°C to 100°C at a constant pressure of 1 atm.Determine the approximate change in internal energy (in cal)of the water.

If an object feels cold to the touch,the only statement that you can make that must be correct is that