Because the formulas for Coulomb's law and Newton's law of gravity have the same inverse-square law dependence on distance, a formula analogous to the formula for Gauss's law can be found for gravity. The gravitational ficld ĝ at a location is the force per unit mass on a test mass mo placed at that location. (Then, for a point mass m at the origin, the gravitational ficld g at some position 7' is j = – (Gym/r²) î.) (a) Compute the flux of the gravitational ficld through a sphcrical surface of radius r, and verify that the gravitational analog of Gauss's law is dÃ= -4TGNMencl· (b) What do you think is the differential form of Gauss's law for gravitation? (c) Determine the gravitational ficld, g, a distance r from the center of the Earth (where r < RE, where RE is the radius of the Earth), assuming that the Earth's density is uniform. Express your answer in terms of GN, the mass of the Earth, МЕ, and Rg.

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Chapter13: Gravitation
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Problem 13.11CYU: Check Your Understanding Consider the density required to make Earth a black hole compared to that...
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Because the formulas for Coulomb's law and Newton's law of gravity have the same
inverse-square law dependence on distance, a formula analogous to the formula for
Gauss's law can be found for gravity. The gravitational ficld g at a location is the force
per unit mass on a test mass mo placed at that location. (Then, for a point mass m
at the origin, the gravitational field g at some position is g = - (GNm/r²)î.)
(a) Compute the flux of the gravitational ficld through a spherical surface of radius
r, and verify that the gravitational analog of Gauss's law is
*, = f i
dà = -4TGNMenel·
(b) What do you think is the differential form of Gauss's law for gravitation?
(c) Determine the gravitational field, g, a distance r from the center of the Earth
(where r < RE, where RE is the radius of the Earth), assuming that the Earth's
density is uniform. Express your answer in terms of GN, the mass of the Earth,
МЕ, and Rp-
Using the results of the problem above, suppose that you were to drill a tunnel all
the way through the Earth, and then drop a ball down the tunnel. Neglecting any
friction/air resistance/cffects due to the rotation of the Earth, cxplain what would
happen to the ball and how long you would have to wait (in minutes!) to get it back!
Hint: consider the force on the ball when it is inside the Earth. Does this form of the
force look familiar? This same method also works for a small charge falling through an
oppositely-charged big ball of charge, of course.
Transcribed Image Text:Because the formulas for Coulomb's law and Newton's law of gravity have the same inverse-square law dependence on distance, a formula analogous to the formula for Gauss's law can be found for gravity. The gravitational ficld g at a location is the force per unit mass on a test mass mo placed at that location. (Then, for a point mass m at the origin, the gravitational field g at some position is g = - (GNm/r²)î.) (a) Compute the flux of the gravitational ficld through a spherical surface of radius r, and verify that the gravitational analog of Gauss's law is *, = f i dà = -4TGNMenel· (b) What do you think is the differential form of Gauss's law for gravitation? (c) Determine the gravitational field, g, a distance r from the center of the Earth (where r < RE, where RE is the radius of the Earth), assuming that the Earth's density is uniform. Express your answer in terms of GN, the mass of the Earth, МЕ, and Rp- Using the results of the problem above, suppose that you were to drill a tunnel all the way through the Earth, and then drop a ball down the tunnel. Neglecting any friction/air resistance/cffects due to the rotation of the Earth, cxplain what would happen to the ball and how long you would have to wait (in minutes!) to get it back! Hint: consider the force on the ball when it is inside the Earth. Does this form of the force look familiar? This same method also works for a small charge falling through an oppositely-charged big ball of charge, of course.
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