Back to Schedule

## Assignment 2

### Due Monday, February 23, in class. Show your work. Have fun.

```1) Fun with complex numbers.  Assume j = sqrt(-1).
Show your work, and reduce/convert to simplest form:

a)  (1-j)2 =

b)  (1-j)/(1+j) =

c)  (-1)-1/4 =

d)  |j2| / |(1-j)2| = abs(j^2) / abs((1-j)^2) =

e)  ln(ej) =

f)  (j-j)j =
(NOTE: (j to the minus j) to the j)

2) Fun with rectangular/polar conversion.  Convert these
to polar, and plot them (except (c))

a)  1 - j =

b)  1 + (√ 3)j = 1 + sqrt(3)j =

c)  x - jy =

d)  (-1)1/4

e)  ejΠ - 1 = exp(jPI) - 1 =

f)  sin(θ) + jcos(θ) = sin(theta) + jcos(theta) =

3)  Use complex exponential identities to show that

cos(A) + cos(B) = 2 cos((A-B)/2)cos((A+B)/2)

How does this relate to question 6 of Assignment 1?

4)  Show that Equation 4.3 from the Cook book solves the differential equation
for the mass/spring/damper.

5)  Find a slinky, bungy cord, big rubber band, or similar springy object.
Find an object of suitable (you'll see later) weight.
Find a timing device (stopwatch or watch with second hand).
Attach one end of the spring to something solid and
relatively unmoveable (like a doorframe, your sleeping roommate,
etc.).  Attach your suitably weighted object to the bottom
of the spring.  Pull your object down, stretching the spring some.
Let go, and count how many oscillations happen in a timed
interval (say, 15 or 30 seconds).  Pull it down a measured
amount, like 12 inches, let go, and time how long it takes
until the oscillations damp to 1/10 of the original amplitude
(1.2 or so inches for an initial displacement of 12 inches).
Try to measure or somehow deduce (look it up on the web if it's
an object you can buy) the weight of the object.  From that,
damping time, calculate the spring constant and damping constant

6)  Change the constants in the masprdmp.c code to reflect your
estimated/calculated constants (from (5) above).  Change the
code so that it synthesizes for a longer time (like a minute).
Recompile, run, inspect the resulting wave in a sound editor and
see if it all makes sense.  Turn in a plot of your synthesized wave
with the axes clearly labeled.

7)  Disconnect your spring from the rigid object, and suspend your
mass from the spring from your hand.  Move your hand up and down
at various rates, slow, faster, really fast, noisily random.
Report what you observe.  Is there a rate at which the mass
oscillates in synchrony with your hand?  Why would this be?

8)  Do something really interesting with this MATLAB Code
by Tae Hong Park, and with MATLAB in general.
Make a 17 second musical statement with it.
Submit as usual and we'll listen and discuss.

```

Back to Schedule