up2 hw ch 20 first law thermo rev

8/12/2019 UP2 HW Ch 20 First Law Thermo Rev

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PHYS-2326: University Physics-II Ch-20 Spring-2013

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Name: ____________________________________

HOMEWORK PROBLEMS Chapter 20: THE FIRST LAW OF THERMODYNAMICS

NOTE:

Show the equations and calculations, and box your answer. Be sure to include the units.

Solve ALL problems. Any four questionsfrom this HW will be graded, and the marks for this HW will

be based on these only.

1. 0.350 kg of water at 20.0C, and 0.300 kg of aluminum at 26.0C are added to a copper

container of mass 0.150 kg which is initially at 100C. The container and contents are insulatedfrom the outside, and reach thermal equilibrium after some time. What is the final temperature of

the container and its contents?

2. How much heat is required to raise the temperature of 50 gram of ice (a) from -20C to its

melting point; (b) convert this to liquid water at 0C; (c) raise the temperature of the resulting

water at 0C to water at 100C; (d) convert the water at 100C to steam at 100C; (e) Raise the

temperature of steam from 100C to 150C.

3. While reproducing Joules experiment (see Figure 20.1 of the text), you use two blocks of

2.00 kg each. The insulated tank is filled with 250 g of water. When the blocks fall through 3.00 m,

what is the increase in the waters temperature?


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4. The temperature of a silver ingot of mass 525 gram increases from 25C to 35C when 1.23

kJ of heat is provided to it. Calculate the specific heat of silver.

5. A vessel contains a large amount of liquid nitrogen at 77.3K (which is also its boiling point).

A 1.00-kg cylinder of copper at 40.0C is dropped into the vessel. How many kilograms of nitrogen

will boil away by the time the copper reaches 77.3 K? (The specific heat of copper is 0.0920

cal/g C, and the latent heat of vaporization of nitrogen is 48.0 cal/g.)

6. When an automobile is stopped by applying the brakes, the kinetic energy of the car

transforms into heat, which raises the temperature of the brakes. If the mass of a car is 1500 kg,

and its steel brakes have a mass of 6.00 kg, calculate the temperature of the brakes when the car

is stopped from a speed of 30 m/s. Assume all the mechanical energy transforms into internal

energy of the brakes, The brakes are originally at 20.0C.

7. (a) Determine the work done on a gas that expands from ito fas indicated in Figure

P20.24. (b) How much work is done on the gas if it is compressed from fto ialong the same path?


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8. A sample of an ideal gas goes through the process shown in Figure P20.30. From Ato B,

the process is adiabatic; from Bto C, it is isobaric with 100 kJ of energy entering the system by

heat; from Cto D, the process is isothermal; and from Dto A, it is isobaric with 150 kJ of energy

leaving the system by heat. Determine the difference in internal energy Eint,BEint,A.

9. A 2.00-mol sample of helium gas initially at 300 K, and 0.500 atm is compressed isothermally

to 2.00 atm. Assume that helium behaves as an ideal gas, find (a) the final volume of the gas, (b)

the work done on the gas, and (c) the energy transferred by heat.

10. The surface of a hot steel ingot taken out of the furnace is 800C. If the ingot is spherical

with a radius of 10 cm, how much heat is it radiating per second.


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11.At noon, the Sun delivers 1000 W per square meter to a blacktop road. If the hot asphalt

transfers energy only by radiation, what is its steady-state temperature?

12. Calculate the amount of heat loss though a glass window made of a single pane of glass

0.100 in. thick, if the temperature inside the room is 70F and outside is 32 F.

13. A bar of steel (iron) has a cross sectional area of 2 cm2. Its two ends are maintained at 0C

and 1000C. Calculate the amount of heat that travels through it in one minute.

up2 hw ch 20 first law thermo rev

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