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Phys 326: Geophysics Question Paper
Phys 326: Geophysics
Course:Bachelor Of Science
Institution: Chuka University question papers
Exam Year:2013
CHUKA
UNIVERSITY
UNIVERSITY EXAMINATIONS
EXAMINATIONS FOR THE AWARD OF DEGREE OF
BACHELOR OF SCIENCE (GENERAL) AND BACHELOR OF EDUCATION (SCIENCE)
PHYS 326: GEOPHYSICS
STREAMS: BSC & BED (SCIENCE) TIME: 2 HOURS
DAY/DATE: MONDAY 22/4/2013 8.30 AM – 10.30 AM
INSTRUCTIONS:
Attempt Question One and any other Two Questions
QUESTION ONE
(a) What is an astronomical unit? [1 Mark]
(b) Express a light year (ly) in metres [2 Marks]
(c) Differnnitate between p and s seismic waves. [4 Marks]
(d) State the three kepler laws of planetary motion. [3 Marks]
(e) State Titins – Bodes law and use it to find the distance of planet plate from the sun.
[3 Marks]
(f) Highlight the two major categories of planets and give two the characteristics of each category . [6 Marks]
(g) What are the earths’ crast and the lithosphere and how are they distinguished. [4 Marks]
(h) What is the geoids? What is the reference ellipsoid? How and why do they differ?
[4 Marks]
(i) What is isostacy? What is an isostatic gravity anomaly? [3 Marks]
QUESTION TWO
(a) Show that Keplers law of equal areas is equivalent of to the law of conservation of angular momentum. [10 Marks]
(b) The ecctricity e of the moons’ orbit is 0.0549 and the mean orbital radius r_l is ? r?_l=(ab)^(1/2) is 384,100 km.
(i) Calculate the leghths of the principal axes a and b of the moons orbit.
(ii) How far is the centre of the earth from the centre of the elliptical orbit?
(iii) Calculate the distances of the mean from the earth at perigee and apogee.
[10 Marks]
QUESTION THREE
(a) A planet with radius R has a portion with uniform density l_m enclosing a core with radius r_c and uniform density l_c. Show that the mean density of the planet l is given by
?l-l?_m/(l_i-l_m )=(r_c/R)^3 [7 Marks]
(b) The bary centre of a star and its planet or of a planet and its mean is the center of mass of the pair. Using the mass radius of primary body and satellite, and the artibaul radius of the satellite as given below, calculate the location of the bary centre of the pair. Does the bary centre lie inside or outside of the primary body? Pluto (mass 1.27×?10?^22 kg, radius 1.37km) and a charon’s (mass 1.9×?10?^21 kg, radius 586km). the radius of charon’s orbit is 19.640 km. [12 Marks]
QUESTION FOUR
(a) Show that the gravitational potential u_e inside a homogeneous uniform solid sphere of radius R at a distance re from its centre is given by u_e=2p/3 60 (?3R?^2-r^2 [10 Marks]
(b) A thin borehole is drilled through the centre of the Earth and a ball is dropped into the borehole. Assume the earth to be a haogenesis solid sphere. Show that the ball will oscillate back and forth from one side of the earth to the other. How long does it take to traverse the Earth and reach the other side? [10 Marks]
QUESTION FIVE
(a) Calculate the maximum gravity anomaly at ground level over a buried anticlinal structure modeled by a horizontal cylinder with radius 1000m and density contrast 200kgm^(-3) when the depth of the cylinder axis is 1500m. [10 Marks]
(b) The peak A of a mountain is 1000m above the level CD of the surrounding plane(plain) , as shown in the diagram below. The density of the rocks forming the mountain is 2800 kgm^(-3,) that of the surrounding crust is 3000kgm^(-3). Assuming that the mountain and its “root” are symmetric above A and that the system is local isostatic equilibrium, calculate the depth of B below the level CD.
A
-------------------
C D
L=2800
L=3000
B
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