An iron cube whose mass is M slides horizontally over a long iron plate
of identical mass. The plate is a rest while the cube has an initial
kinetic energy K. Friction brings the cube to rest before its base reaches
the plate's boundary. Everything is in the vacuum and the internal energy,
dU, added to both pieces of iron is not lost. [In principle, dU can be
calculated from the observed change of temperature but no thermometer is
available.] Which of the following is correct and why?
1. The internal energy dU is equal to K.
2. Only part of K goes into dU, the rest is used to do work W=R*x, where
R is the force of kinetic friction and x is the distance the cube
slides before comming to rest.
3. Neither of the above is correct.
I am really confused in this situation. My frame of reference (for K and x)
is attached to the plate.
Make sure I understand you.
Ludwik Kowalski