PHY
2O2O
Homework Set
#I2
FaJl 2014
Name:
Due: At the start of class on FYiday, Nov. 21. Not
5 minutes after the sta.rt of class.
If you just give an answer without showing how you arrived
at that a,nswer, then you will
get no credit for the problem.
1' (lpt) Two guitar
strings are identical except that one has slightly more
tension in the
string than the other one has. when one string is plucked
ii
vibrates at 300 Hz, and.
when the other string is plucked it vibrates at got
Hz. When they are both plucked
simultaneously, a"nd you carefully listen to the sound, you
hear the a"rnplitude of the
g-o-}trd slowly getting louder a.nd then sofber, louder then sofber
...
What is the ,,beat frequency" of this sound?
2' (2pts) You are standing
next to the mnway at an airport, when a jet pla.ne flies right
"t
r igh-t"ch jet plane
having a frequency of
over your head at one half the speed of sound. The jet piuo"
i,
that has engines that only makes sound that the pitot nlars as
400H2
(a) what frequency do you hear when the jet is moving directly toward
you?
(b) what frequency do you hear when the jet is moving directly
away from you?
3' In class, I had a plastic rod that I first rubbed with
a wool rag and then placed on top
of a post that allowed the rod to rotate in a horizontal circle.
(a) (tpt) Then I picked up a glass rod and rubbed it with a piece of silk.
When I
held the glass rod near the end of the plastic rod., was the
rod
attracted
flastic
or repelled or was there no interaction at all?
(b) (tpt) Nexb I put an aluminum rod on the post, and when I brought the plastic
rod (a.fter rubbing it with the wool again) close to the end of the aluminum
rod was the aluminum attracted or repelied from the plastic or was
there no
interaction at all?
(c) (1pt) Finally, with the aluminum rod still on the post, I brought the glass rod
(a'fter rubbing it with the silk again) close to the end of the aluminum
rod and
was the aluminum rod attracted or repelled from the glass or was
there no
interaction at all?
4' Two resistors Rr :
diagram.
3
ohm and Rz
:
6ohm are in seri,es in a circuit, as shown in the
bn
Xv
3J;t(a) (2pt) what is the effective
resistance of the two resistors together?
(b) Using ohm's law, what is the current tbrorrgh the battery?
(c) (Zpt) The two resistors Rr : 3 Ohm and R2 : 6 Ohm a,re now parallel
in
in
a circuit, as shovrn in the diagra,rn. What is the effective resistance
of the two
resistors together?
*E6n
(d) And'sing ohm's law what is the current through the battery?