To David B, Leigh P, and everybody else who wants to answer.
Now that we all understand everything about the first law (ha, ha, ha)
let us suppose that you are a teacher in an introductory physics course.
The following problem is presented to your students, for example in an
AP physics exam. As you see, it is the same situation which triggered
our debate. But questions are different. Please show what one of your
best students should be able to do in about 30 minutes. A pocket
calculator is allowed.
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An iron cube of mass m=1 kg slides horizontally over a long iron plate
which remains at rest. The mass of the plate is 99 kg. The specific heat
capacity of iron is 470 J/(Kg*K), the coefficient of kinetic friction is
0.57. The initial kinetic energy of the cube is 50 J. Friction brings the
cube to rest before its base reaches the plate's boundary. Everything is
in the vacuum.
1) What is the initial speed of the cube? How far will it slide?
(hint: g=9.80 m/s^2)
2) Calculate the change of temperature of iron (both pieces treated as
one object). What assumptions are you making to find the answer?
3) How much heat is generated? How much work is done? Explain what happens
to the initial kinetic energy of the iron cube.
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Ludwik Kowalski
P.S.
Are words "generated" and "done" acceptable? What words would be better?
Keep it simple, please.