Py 120 Test 3 Spring 1998
Part A: Interactive Type Problem. (20 pts)
1) A traveling pressure wave is shown on the monitors in the front of the room. An
observer is stationed at a distance D from the wave source and measures the pressure as a
function of time. Her measurement of the pressure variation as a function of time is shown
above for a two milliseconds time duration. Assume that the speed of sound is 330 m/s.
Answer the following:
a) What is the average frequency of the sound heard?
b) What beat frequency is heard?
c) Write an equation for the pressure variation as a function of time at D.
d) Assume that intensity is momentarily zero at D. Are there other points
where the intensity is a maximum at that same instant? If so, where?
Part B: Concept problems. (20 pts each.) These are short but you must still GIVE YOUR REASONS.
A 500 gram rock is suspended at the end of a 1 meter stick as shown above. The stick is
marked in 25 cm increments. Where is the center of mass of the system? How much does the
meter stick weigh?
Part C: Textbook problems (40 pts total.)