Exam 11: Energy in Thermal Processes

An inventor develops a stationary cycling device by which an individual,while pedaling,can convert all of the energy expended into heat for warming water.What minimum power must be generated if 210 g water (enough for 1 cup of coffee)is to be heated in 14.0 min from 26.0°C to 84.0°C? (1 cal = 4.186 J,the specific heat of water is 4 186 J/kg⋅°C)

Carly places one end of a steel bar in a Bunsen flame and the other end in an ice cube.By what factor is the rate of heat flow changed when the bar's cross-sectional area is doubled?

A hot (85.0°C)lump of metal has a mass of 210 g and a specific heat of 0.250 cal/g⋅°C.John drops the metal into a 345-g calorimeter containing 95 g of water at 21.3°C.The calorimeter is constructed of a material that has a specific heat of 0.100 cal/ g⋅°C.When equilibrium is reached,what will be the final temperature? c_water = 1.00 cal/g⋅°C.

A machine gear consists of 0.14 kg of iron and 0.19 kg of copper.How much total heat is generated in the part if its temperature increases by 35.0 C°? (Specific heats of iron and copper are 450 and 390 J/kg⋅°C,respectively. )

A solar heating system has a 25.0% conversion efficiency;the solar radiation incident on the panels is 800 W/m².What is the increase in temperature of 25.0 kg of water in a 1.00-h period by a 3.40-m²-area collector? (c_w = 4 186 J/kg⋅°C)

A 0.0040-kg lead bullet is traveling at a speed of 220 m/s when it embeds in a block of ice at 0°C.If all the heat generated goes into melting ice,what quantity of ice is melted? (L_f = 80 kcal/kg,the specific heat of lead = 0.03 kcal/kg⋅°C,and 1 kcal = 4 186 J)

In typical calorimetry problems,what is the usual conservation law being used?

A 38.0-kg cheetah accelerates from rest to 26.0 m/s in 3.00 seconds. Assume the cheetah converts food energy to mechanical energy with an efficiency of 25.0% -At what average rate is the cheetah burning Calories?

How does the heat energy from the Sun reach us through the vacuum of space?

Pennies used to be made of copper,but now they are made of copper-coated zinc.If one were to do a precise calorimetry experiment to determine the specific heat of the new pennies,what would the result be?

If the surface temperature of the Earth is 290 K and that of the Sun is 6 000 K,assuming the same emissivities,what is the ratio of the energy radiated per square meter of the Earth to that of the Sun?

The inside of a house is at 20°C on an early morning when the temperature outside is 15°C.The next morning the inside temperature is the same but the outside temperature is now 10°C.How much does the energy per unit time lost by conduction through the walls,windows,doors,etc. ,change for the house from the first morning to the second one?

Two stars,A and B,have the same emissivity,but the radii and surface temperatures are different with R_A = 0.5R_B,and T_A = 2T_B.Assuming the temperature of space to be negligible,which star radiates the most energy per unit time?

Which type of heating causes sunburn?

The thermal conductivity of copper is 397 J/s⋅m⋅°C and of silver is 427 J/s⋅m⋅°C.A rod of each material is used as a heat conductor.If the rods have the same geometry and are used between the same temperature differences for the same time interval,what is the ratio of the heat transferred by copper to the heat transferred by the silver?

If a 1 050-kg car was moving at 25 m/s,what would be its kinetic energy expressed in the unusual (for kinetic energy)units of calories? (1 cal = 4.186 J)

The use of fiberglass insulation in the outer walls of a building is intended to minimize heat transfer through the wall by what process?

A 1.9-m² Thermopane window is constructed by using two layers of glass 4.0 mm thick,separated by an air space of 5.0 mm.If the temperature difference is 25.0 °C from the inside of the house to the outside air,what is the rate of heat flow through this window? (Thermal conductivity for glass is 0.840 J/s⋅m⋅°C and for air 0.023 4 J/s⋅m⋅°C. )

A silver bar of length 25.0 cm and cross-sectional area 1.25 cm² is used to transfer heat from a 80.5°C reservoir to a 0°C block of ice.How much ice is melted per second? (For silver,k = 427 J/s⋅m⋅°C.For ice,L_f = 334 000 J/kg. )

A waterfall is 128 m high.What is the increase in water temperature at the bottom of the falls if all the initial potential energy goes into heating the water? (g = 9.8 m/s²,c_w = 4 186 J/kg⋅°C)