TEACHER'S TEACHERS'S TEACHER'S TEACHER'S
Ken Cheney
10/28/2005
5:03/C0
Physics 31A Test Six
1. ELEPHANT HAULING
How many meters will a 12,000 meter long steel cable .000071
square meters in cross section stretch when picking up a 15,000 newton
elephant? Y=20E10 n/(m squared)
15,000*12,000/(.000071*20E10)
a. 4.67, b. 7.75, *c. 12.7, d. 14, e. 38.1
2. SHORT WAVE EQUATION
Derive the equation for waves: wave length = velocity/frequency.
Explain and sketch.
3. TEMP AND BRIDGES
If a 1,100 meter bridge is built at a temperature of 27 degrees
centigrade, how many meters must be allowed for thermal contraction
when the temperature goes to -24 degrees?
ALPHA=11E-6 1/DEGREES CENTIGRADE
1,100*(27+24)*11E-6
a. .25, b. .375, c. .506, *d. .617, e. 1
4. WATER POWER
A cylinder with a piston adjusts the volume so as to maintain a
constant pressure of one atmosphere. Initially there are two molecules
of hydrogen for each molecule of oxygen inside the cylinder. The gases
burn and produce water vapor. Find the final volume, in liters, if the
temperature increases from 20 to 620 degrees centigrade, and the
initial volume was 110 liters.
110*2*(620+273)/(3*(20+273))
a. 89.1, b. 167, *c. 224, d. 408, e. 874
5. ROCK
If one speaker produces 100 dB at a distance of 24 feet how many
speakers are required for 120 dB at 250 feet? Assume that the waves
expand in the same way.
250*250*10**(12-100/10)/24/24
*a. 10,900, b. 15,300, c. 22,300, d. 32,300, e. 46,000
6. DARTH VADER
Darth Vader is running toward you in the pitch black night. You
plan to calculate his approach velocity by mixing the sound of his
breathing (known to be 54 Hz) with a 54 Hz frequency source which you
carry with you at all times. If you count 7.6 beats/sec what is his
Physics 31A Test Six - Ken Cheney - V. 5:03/C COPY 0 PAGE 2
approach velocity in m/s? The speed of sound is 300 m/s. There are two
answers depending on whether you add or subtract the beat frequency,
add.
300*(1-54/(54+7.6))
a. 14.7, b. 20.9, c. 28.1, *d. 37, e. 48.7
7. BRIDGE 1 and 2
A 80 meter long bridge consists of cables which act like a string
of 580 kg/m linear density with a tension of 4,400 N. If the bridge is
over a hole in the earth, how deep must the hole be so the frequency of
the first overtone of the bridge resonates with the second overtone of
the hole? Velocity of sound =300 m/s. Velocity of waves on a string =
SQR(tension/ linear density)
5*80*300/(4*SQR(4,400/580))
a. 2,250, b. 7,080, *c. 10,900, d. 315,000, e. 6.53 E6
8. DURIVE GAS LAW
Durive the Gas Law starting with the force produced by molecules
and ending with PV=nRT. Explain carefully. You can use
proportionalitys instead of integrals during the derivation.