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Unformatted text preview: f Physics 70
ﬂ Fall 2000
Midterm 2
R. Packard Name: SID Discussion section day and time Work all the problems. They are weighted equally. If you don’t understand
the question ask the proctor for clariﬁcation. Do not perform any numerical work until you have a “boxed” algebraic answer. Do a dimension check on
your ﬁnal answer. Total 1. An engineer travelling on a train at v=150km/hr sees two lamps on the
ground ﬂash at the same time. In the rest frame of the lamps, they are
spaced a distance d=100m apart, parallel to the train tracks. A) Which of the lamps, the ﬁrst one the train passed (#1) or the second
one (#2), ﬂashed ﬁrst in the rest ﬂame of the lamps?
B) How much earlier did it ﬂash? 2. In the Compton effect a 0.1nm photon strikes a free electron at rest, in a
headon collision and knocks it in the forward direction. The rebounding
photon recoils directly backwards. Use conservation of (relativistic) energy and momentum to compute the kinetic energy of the recoiling
electron. 3. Suppose an electron was bound to a proton as in the hydrogen atom, by
the gravitational force rather than the electric force. What would then be
the energy of the ﬁrst Bohr orbit? G=6.67x10'“(SI units),
me=9x10'3‘kg, mp=1836me. 4. A particle of mass m is bound in a simple harmonic oscillator potential,
V=kx2/2. Use the uncertainty relation to estimate the average ground
state energy.[Hint: for a symmetric potential, the average value of p2=(Ap)2, and the average value of x2 is (Ax)2. Write the total average
energy and minimize it.] ...
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This note was uploaded on 05/07/2010 for the course MATH 1 taught by Professor Ribbet during the Spring '10 term at The University of British Columbia.
 Spring '10
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