l. A long hollow metal pipe with an external diameter of l m and an internal diameter of 80 cm is buried at 5 m depth in the ground with its axis horizontal. Calculate the gravity anomaly at the surface along AA' at 2 m intervals from -20 m to + 20 m when the pipe is lled with air. You should assume that the pipe is surrounded by soil. Use the following density values: metal = 6 gr'cmj and soil = 2.0 gfcmj. (15 points} X=0 A A' Soil 2. A mountain belt is 4 km above the sea level and in Airy isostatic equilibrium. Assume the density as 2800 kgfm3 for the crust and 3300 kgfm3 for the mantle, and answer the two following questions. (1}. Assume the normal crust is 35 km thick, what is the Moho depth under the mountain? (5 ms) (2} During a period of erosion. a 2 km thickness of material is removed from the mountain belt. When the new isostatic equilibrium is achieved, how high is the mountain? {5 pts) (3} How much material need to be eroded to bring the mountain eventually down to the sea level? [5 pts)