GENERAL PHYSICS I               SAMPLE EXAM  CH's 10,11

USEFUL CONSTANTS for WATER: c = 4186 J/kg AoC = 1.00 cal/gm A oC ,
Lf = 3.33x105 J/kg = 79.7 cal/gm
Lv = 2.26x106 J/kg = 540 cal/gm
ICE: c = 2090 J/kg A oC = 0.500 cal/gm A oC
STEAM: c = 2010 J/kg AoC = 0.480 cal/gm A oC
pressure: 1.00 atm = 1.01 x 105 N/m2

1]    A semicircular area of radius 10.00 cm is cut into the side of a large flat piece of
steel at 20.00oC.  What is the final total area of the semicircle if the piece of steel is
heated to 200.0oC ?    [ for steel, ( a = 11.0 x 10-6 / oC ) ]

2]   What mass of ice that is initially at -15.0oC is needed to cool 250 gm of water in a
150 gm glass container from 20.0oC down to 5.0oC ?  [for glass, c = 0.20 cal/(g oC) ]

3]    Suppose your skin has an emissivity of 0.70 and that 0.27 m of bare skin is exposed to
the air which is at a temperature of 20oC.  Assume your skin is at a temperature of 37oC and
determine the net power radiated by this exposed area of skin.

1]   The typical speed of sound in air is given as  340 m/s.  Assume the molar mass of air to be
29.0
gm/mole.   At what temperature (in oC ) will the air molecules have an average (or rms)
speed equal to the typical speed of sound?

ANSW:     135 K    or   -138 Celsius

2]     A 3.50 liter tank of oxygen is at a temperature of 20.0 oC and a pressure of 25.0 atmospheres.

If the molecular mass of oxygen is 32.0 gm/mole,  what is the mass of oxygen in the tank?

ANSW:    0.116 kg

4]     If 14.4 grams of steam at 150 oC are added to 300 grams of water at 10.0 oC , what final equilibrium
temperature is reached ?

ANSW:   40 degrees Celsius

3]    The door on a wood stove used for heating a room is a square iron plate (25 cm on a side) with a
thickness of 1.25 cm.  The temperature inside the stove is 250 oC while the temperature on the outside
door face is 200 oC.  How much heat passes through the door in 1 hour?   (k = 79.5 J/s
·m·oC for iron)

ANSW:   7.16 x 10(7) J

4]    Air has a much lower thermal conductivity than foam insulation.  Why then do we put foam
insulation in the walls and ceilings of houses?

Answer:  To prevent convection.  It is "dead" air spaces that are needed.  In open wall and ceiling
spaces the air will convect heat from inner "warm" walls to the outer "cold" walls.

MULTIPLE CHOICE QUESTION

1)  Studies of the expansion of metals show that different metals

A) expand at different rates when heated
B) expand at different rates when cooled
C) expand at the same rates when heated
D) expand at the same rates when cooled
E)  don't expand until a certain temperature is reached

2)  When objects are at different temperatures

A)  energy is not transferred
B)  energy is transferred from the cooler object to the warmer object
C)  energy is transferred from the warmer object to the cooler object
D)  the objects transfer energy to their surroundings, but not to each other

3)  On a sunny day, your clothing becomes hot because

A)  light is absorbed and changed to energy in the form of heat
B)  light and energy are reflected off of your clothing
C)  light and energy are transmitted from your clothing
D)  energy is transmitted and light is reflected from your clothing

4)  An assumption below that is not a part of those made for the kinetic theory of gases is

A) the number of molecules is small
B) the molecules obey Newton's laws of motion
C) collisions between molecules are elastic
D) the gas is a pure substance
E) the average separation between molecules is large compared to their dimensions

5)  An amount of energy is added to ice, raising its temperature from  -10 C  to -5 C.  A larger amount of energy
is added to liquid water (of the same mass as the ice) to raise its temperature from 15 C to 20 C.  From these
results we can conclude that,

A)  overcoming the latent heat of fusion of ice requires an input of energy
B)  the latent heat of fusion of ice delivers some energy to the system
C)  the specific heat of ice is less than that of water
D)  the specific heat of ice is greater than that of water