University of California, San Diego
Physics 1b - Thermodynamics, Electricity & Magnetism
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Physics 1B - Tutorial #2
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- Very cold ice is placed in a closed container. Heat is then applied to the
container. Below is a graph of the temperature inside the container
plotted against the amount of heat delivered to the system.
- Describe what is happening to the substance inside the container from
point A to point F.
- Put temperature scales in Celsius on the vertical axis.
- If the heating rate is constant (dQ/dt = constant), compare the time it
takes to heat from B to C to the time it takes to heat from D to E.
- Materials A and B have equal densities. But A has twice the specific heat
of B. You have two 100 g cubes made of materials A and B.
- Cube A, initially at 0°C, is placed in good thermal contact
with cube B, initially at 100°C. Both are placed in a
well-insulated container. What is the final temperature?
- Cubes A and B are both heated to 200°C, and then placed in
room temperature environment. Which one cools faster?
- A thermometer is laid out in direct sunlight. Does it measure the
temperature of the air, of the sun, or of something else?
- The inside of an oven is at 400° F. But you can still put
your hand in the oven as long as you don't touch anything. But since the
air inside the oven is also at 400°F, why isn't your hand
burned just the same? What if you leave your hand in the oven for a
long time (e.g. 2 hours)?
- While jogging, an average 65 kg student generates thermal energy at a
rate of 300 W (about 0.4 horse power). To maintain a constant body temperature
of 37°C, this energy has to be dissipated by perspiration or
other mechanisms.
- If these mechanisms failed and the heat couldn't flow out of
the student's body, for how long could a student run before irreversible body
damage could occur? (Protein structures in the body are irreversibly damaged
at 44°C or above. The specific heat capacity of a typical human
body is 3480 J/kg.K, slightly less than that of water.)
- If the heat loss is by sweat evaporation only, calculate the volume of
water evaporated per minute (latent heat Lv = 539 cal/g). How many
liters of water are needed to
compensate the water loss of a two hour jog? What other heat loss mechanisms
do you think may be important for a runner?

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Gene Smith
Last
modified: Tues., 11 Apr 2000