Physics 114 –Morning
Session, Summer 2004
This is an in-class work,
to be turned in at the end each discussion session. No points when
absent.
Use provided space to show
your work only, use back page for notes
Student’s Name:_______________________
Team #______________
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1.-
(a) If system A is not in thermodynamic (TD) equilibrium with system B,
and B is not in equilibrium with C, can you draw any conclusions about the
temperatures of the three systems? Circle an answer.
Yes
No
(b) A thin layer of glass
does not offer much resistance to heat conduction. Yet double-glazed windows
provide substantial energy savings. Why? Answer in one
phrase.
(c) What’s the dominant
mode of heat loss from a red-glow burner? ________________What’s the dominant
mode of heat transfer from burner to pan
______________________; from bottom of pan to top of water
surface_________________________
2.-
Specific Heat. A piece of
copper at 300oC is dropped into 1kg of water at 20oC, if
the equilibrium temperature is 250C, what is the mass of the copper.
Hints: heat loss by copper equals heat
gain by water, use specific heat values from table.
3.-
Heat Transfer. A 8m x 10m
basement is built on a concrete slab 25cm thick. What is the heat loss rate
through the concrete floor if indoor temperature is maintained at
20oC while the ground is at 10oC? Hints: use value for thermal conductivity of
concrete from table.
4.-
(a) Why
are you supposed to check the pressure in a tire when the tire is cold? One
phrase answer:
(b)
Two different gases are at the same temperature, and both are at low densities
that they behave like ideal gases. Do their molecules have the same thermal
speeds? Explain in one phrase.
(c)
Why do we use the triple point of water for thermometer calibration? Why not
just the melting point or the boiling point?
5.-
Gases. A dorm room measures
3m x 3m x 2m, (a) how many air molecules does it contain (hint: assume air is an ideal
gas)
(b) What is the total
translational KE of these molecules? (hint:in an ideal gas, thermal energy provide
translational KE)
(c) How is this energy
compared to the KE of a 2000kg car going at 108km/h?
6.-
Phase Changes. A 250g piece
of ice at 0oC is placed in a 500W microwave oven which runs for 5
min. What is the temperature at the end of this time? (Hint: check if total enerfy supplied by oven
can melt the ice and then increase its temperature, use heat of transformation
and specific heat for ice and water from tables)
7.-
(a) You
bring a pot of water to boil, then forget about it. Ten minutes later you come
back to the kitchen to find the water still boiling. What’s its
temperature?
(b)
Why is it the specific heat at constant pressure greater than at constant
volume?
(c)
When a system is in TD equilibrium -What’s the average energy per molecule
_______________
What’s
the theorem you used __________________
8.-
TD Processes: Isothermal. How
much work does it take to compress 25 mol of an ideal gas to half its original
volume while maintaining a constant temperature of 300 K? (Hint: for an ideal gas, the work done along
an isotherm is proportional to
thenatural log of
volumes)
9.-
TD Processes: Adiabatic. A
bike pump is a 30cm long cylinder with the handle all the way out. The pump
contains air (γ=1.4) at 20oC. If the pump outlet is blocked and the
handle pushed until the internal length of the pump cylinder is 10cm, by how
much does the air temperature rise? Assume no heat is lost. (Hint: adiabatic PVγ=constant,
write P in term of T using ideal gas
equation)