PHYS 1301 Section 001
Final Exam
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Fall 2009 W. Wayne Kinnison
Final Exam
SOLUTIONS
Physics 1301 Section 001
Print your name (very legibly) on EACH PAGE of paper that you turn in including this test sheet. Staple all
pages including the test sheet together. Be sure to write legibly for maximum credit.
Concept Questions (Answer all six (6)—5 points each):
1.
You have learned this semester that energy is always conserved in any process where no external
forces are acting on the system. However, the total kinetic energy of two cars measured before and
after a collision is not the same. How then is the concept of energy conservation reconciled with
what happens in an automobile collision?
There are two issues. One is that kinetic energy is not conserved but the sum of kinetic and potential
energy is what is conserved. The other is that the total mechanical energy (kinetic and potential) are
only conserved if there is no external work.
So on the one hand, some of the total kinetic energy is converted to heat, sound, potential energy in
the form of bent parts, etc. So kinetic energy would not be expected to be conserved.
Second, there are external forces involved in that some work goes into deforming the automobiles,
making noise, mass changing because parts fell off, etc. Due to the external energy or forces, the
total kinetic energy is not conserved.
2.
Is friction a conservative or non-conservative force? Explain your answer.
It is a non-conservative force. It is always directed opposite to the direction of motion.
Consequently, movement around a closed path always requires non-zero work.
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