Exam 11: Energy in Thermal Processes

A person has a thermal conductivity of 0.18 W/m·K between his inner core and his skin with an effective shell thickness of 1.30 cm between his core and skin.If his inner core is at the normal 98.6°F,and his skin has a surface area of 1.62 m²,what will be his rate of loss of thermal energy due to conduction through his skin if his skin temperature is 28.3°C?

The filament temperature of a light bulb is 2 100 K when the bulb delivers 40.0 W of power.If its emissivity remains constant,what power is delivered when the filament temperature is 2 500 K?

A swimming pool heater has to be able to raise the temperature of the 50 000 gallons of water in the pool by 12.0 C°.How many kilowatt-hours of energy are required? (One gallon of water has a mass of approximately 3.8 kg and the specific heat of water is 4,186 J/kg⋅°C. )

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.How much mechanical energy is required to increase the temperature of 200 g of water (enough for 1 cup of coffee)from 18°C to 94°C? (1 cal = 4.186 J,the specific heat of water is 4 186 J/kg⋅°C)​

Which of the following has the highest specific heat?

How many calories are equal to four BTU? (One calorie = 4.186 J,one BTU = 1 054 J. )

Dmitri places one end of a copper rod in a heat reservoir and the other end in a heat sink.By what factor is the rate of heat flow changed when the temperature difference between the reservoir and sink is tripled?

A 4.00-g lead bullet is traveling at a speed of 200 m/s when it embeds in a wood post.If we assume that half of the resultant heat energy generated remains with the bullet,what is the increase in temperature of the embedded bullet? (specific heat of lead = 0.0305 kcal/kg⋅°C,1 kcal = 4 186 J)

A 3.00-kg copper rod is 45.0 cm long at 24.8°C.If 45 000 J are transferred to the rod by heat,what is its change in length? c_copper = 387 J/kg⋅°C and α_copper = 17.0 × 10−⁶/°C.

Iced tea is made by adding ice to 1.9 kg of hot tea,initially at 90.0°C.How many kg of ice,initially at 0°C,are required to bring the mixture to 15.0°C? (L_f = 3.33 × 10⁵ J/kg,c_w = 4 186 J/kg⋅°C)

A 10.0-kg piece of aluminum (which has a specific heat of 900 J/kg⋅°C)is warmed so that its temperature increases by 6.0 C°.How much heat was transferred into it?

When a wool blanket is used to keep warm,what is the primary insulating material?

​A typical avocado has 180 Calories.If all this energy could be used to lift a bucket of water weighing 40 N,through what vertical distance could the bucket be lifted? (1 calorie = 4.184 J and 1 Calorie = 10³ calories)

On a sunny day at the beach,the reason the sand gets so hot and the water stays relatively cool is attributed to the difference in which property between water and sand?

In cloud formation,water vapor turns into water droplets which get bigger and bigger until it rains.This will cause the temperature of the air in the clouds to

What temperature increase is necessary to increase the power radiated from an object by a factor of 8?​

A 140-g block of copper is taken from a kiln and quickly placed into a beaker of negligible heat capacity containing 290 g of water.The water temperature rises from 6.8°C to 26.8°C.Given c_Cu = 0.10 cal/g⋅°C,and c_water = 1.00 cal/g⋅°C,what was the temperature of the kiln?

At high noon,the Sun delivers 990 W to each square meter of a blacktop road.What is the equilibrium temperature of the hot asphalt,assuming its emissivity e = 1? (σ = 5.67 × 10−⁸ W/m²⋅K⁴).

As I use sandpaper on some rusty metal,the sandpaper gets hot because:

Two 0.95-kg masses,one aluminum and one tin,both at 80.0 ^$\circ$ C,are placed in 1.00 kg of water at 20.0 ^$\circ$ C.What is the equilibrium temperature of the system? The specific heats of aluminum and tin are 900 J/kg ^$\circ$ C and 227 J/kg ^$\circ$ C,respectively.