Physics 2130
Midterm Examination
Spring 2007
Name:
ID #:
1- An iron anchor of density 7880.00 kg/m3 appears 174 N lighter in water (density 1000
kg/m3) than in air (density 1.2 kg/m3). (a) What is the volume of the anchor? (b) How
much does it weigh in air?
Wair  W  f bair
Wwater  W  f waterr
Wair  Wwater  f bwater  f bair  174 N
174 N  Vg (  water   air )
V 
174
 0.01775m 3
9.81(1000  1.2)
Wair  W  f bair  Vg (    air )  0.01775(9.81)(7880  1.2)  1372 N
2- A cylindrical tank with a large diameter is filled with water to a depth D = 0.42 m. A
hole of cross-sectional area A = 7.1 cm2 in the bottom of the tank allows water to drain
out. (a) What is the rate at which water flows out, in cubic meters per second? (b) At
what distance below the bottom of the tank is the cross-sectional area of the stream equal
to one-half the area of the hole?
1 2
v  gh  v  2 gh  2(9.81)(0.42)  2.87m / s
2
Av  A1v1 
1
Av1  v1  2v  5.74m / 2
2
1 2
5.74 2  2.87 2
2
(v1  v )  gh  h 
 1.26m
2
2(9.81)
Physics 2130
Midterm Examination
Spring 2007
Name:
ID #:
3- What is the lowest frequency for standing waves on a wire that is 10.8 m long, has a
mass of 233 g, and is stretched under a tension of 299 N?
f 
v


 /
2L

299 /(0.233 / 10.8)
 5.45Hz
21.6
4- Two point sources S1 and S2 emit sound of wavelength λ = 2.00 m. The emissions are
isotropic and in phase, and the separation between the sources is d = 16.0 m. At any point
P on the x axis, the wave from S1 and the wave from S2 interfere. What is the phase
difference at P? Assume that P is a distance x from S1. What kind of interference do we
expect as x tends to infinity?
L  x 2  d 2  x
2L


As x tends to infinity, L  x 2  d 2  x  x  x  0 , therefore we have constructive
interference.
5- A window washer attempts to lean a ladder against a frictionless wall. He finds that the
ladder slips on the ground when it is placed at an angle of less than 75° to the ground but
remains in place when the angle is greater than 75°. The coefficient of static friction
between the ladder and the ground:
1- is about 0.13
2- is about 0.27
3- is about 1.3
4- depends on the mass of the ladder
5- depends on the length of the ladder
Physics 2130
Midterm Examination
Spring 2007
Name:
ID #:
6- A cube with edges exactly 2 cm long is made of material with a bulk modulus of 3.5 ×
109 N/m2. When it is subjected to a pressure of 3.0 × 105 Pa its volume is:
1- 7.31 cm3
2- 7.99931 cm3
3- 8.00069 cm3
4- 8.69 cm3
5- none of these
7- A 0.25-kg block oscillates on the end of the spring with a spring constant of 200 N/m.
If the system has an energy of 6.0 J, then the maximum speed of the block is:
1- 0.06 m/s
2- 0.17 m/s
3- 0.24 m/s
4- 4.9 m/s
5- 6.9 m/s
8- The sound level at a point P is 14 db below the sound level at a point 1.0 m from a
point source. The distance from the source to point P is:
1- 4.0 cm
2- 20.2 m
3- 2.0 m
4- 5.0 m
5- 25 m
9- Two stationary tuning forks (350 and 352 Hz) are struck simultaneously. The
resulting sound is observed to:
1- beat with a frequency of 2 beats/s
2- beat with a frequency of 351 beats/s
3- be loud but not beat
4- be Doppler shifted by 2 Hz
5- have a frequency of 702 Hz