Group Work The 2004 Tour de France’s Alpe d’Huez time trial was a climb with its finish 1200 m higher than the start. The winner, Lance Armstrong, and his gear had a combined mass of 84 kg . The work Lance had to do was ( 84 kg )( 9.8 N/kg )( 1200 m ) = about 10 6 J .
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The work Lance had to do was
(84 kg)(9.8 N/kg)(1200 m)= about106 J.
Muscle is about 20% efficient, so Lance had to deplete 5 times as much potential energy as the work he produced. How much energy did he consume?
How much of the energy he consumed was not converted to work?
Heat and Phase Changes
Our interaction with the world of the small
What is work?
James Joule’s life-long obsession
Identical effects of adding heat to a system and doing work on it.
Source: Griffith, The Physics of Everyday Phenomena
When heat is added to an object, how does the object’s energy change?
per mode of motion.
When a red-hot piece of iron is dropped into a bucket of water, the water
increases its temperature.
increases its internal energy.
receives heat from the iron.
all of the above.
C = q/DT = mc
DT = q/(mc)
where m is the object’s mass and c is its specific heat.
Hint: What is the formula for specific heat?
If all the non-work energy he converted in the Alpe d’Huez climb stayed in his 75-kg body, how much would his body temperature have risen?
When are the molecules’ potential energies highest?
Solid < Liquid <Gas
The heat q needed to vaporize a mass m of water is
q = m (2.255 106 J/kg).
Solve for mass m and substitute in the values.
Why most processes are irreversible