3. Let's imagine that the earth is shrinking and we want to escape before it is too late. Let's set up some notation: R: the radius of Earth ME : the mass of Earth m : your mass G : the universal gravitational constant c: the speed of light Note that, since Earth is shrinking, R is not constant, but Mg is constant (the values of ME, G and c are available on Wikipedia). In this question, we will compute the velocity needed to escape Earth and the radius of (shrunken) Earth for which even light cannot escape (when Earth becomes a black hole). In fact, all of the related formulae are well known and the purpose of this question is to justify our work using what we have learned in this course so far. (a) The work (energy) W needed to free yourself from Earth when its radius is R metres is W = GME m dh. Show that this improper integral is equal to ‚ME m R

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3. Let's imagine that the earth is shrinking and we want to escape before it is too late. Let's
set up some notation:
R: the radius of Earth
MẸ : the mass of Earth
m: your mass
G : the universal gravitational constant
c: the speed of light
Note that, since Earth is shrinking, R is not constant, but MẸ is constant (the values of ME,
G and c are available on Wikipedia). In this question, we will compute the velocity needed
to escape Earth and the radius of (shrunken) Earth for which even light cannot escape (when
Earth becomes a black hole). In fact, all of the related formulae are well known and the
purpose of this question is to justify our work using what we have learned in this course so
far.
(a) The work (energy) W needed to free yourself from Earth when its radius is R metres is
w = G
ME m dh.
h2
R
Show that this improper integral is equal to
GME m
R
Transcribed Image Text:3. Let's imagine that the earth is shrinking and we want to escape before it is too late. Let's set up some notation: R: the radius of Earth MẸ : the mass of Earth m: your mass G : the universal gravitational constant c: the speed of light Note that, since Earth is shrinking, R is not constant, but MẸ is constant (the values of ME, G and c are available on Wikipedia). In this question, we will compute the velocity needed to escape Earth and the radius of (shrunken) Earth for which even light cannot escape (when Earth becomes a black hole). In fact, all of the related formulae are well known and the purpose of this question is to justify our work using what we have learned in this course so far. (a) The work (energy) W needed to free yourself from Earth when its radius is R metres is w = G ME m dh. h2 R Show that this improper integral is equal to GME m R
Your justification should show all necessary steps of the computation including the defi-
nition of the improper integral.
(b) By the Work-Energy Principle, we know that
1
w = zmv,
where v is the velocity at which you're escaping Earth (escape velocity). Using this
equation, show that
2GME
v =
(c) Our result from part (b) tells us that, as Earth shrinks, we need a larger and larger
velocity to escape. Find the radius of (shrunken) Earth, RB, for which even light cannot
escape (this is known as the Schwarzschild radius of Earth). Hint: Compute Rg by using
the fact that it occurs exactly when the escape velocity is equal to the speed of light c.
Your answer should be an expression in terms of G, ME, and c. (You may find that RB
is about 9mm.)
Transcribed Image Text:Your justification should show all necessary steps of the computation including the defi- nition of the improper integral. (b) By the Work-Energy Principle, we know that 1 w = zmv, where v is the velocity at which you're escaping Earth (escape velocity). Using this equation, show that 2GME v = (c) Our result from part (b) tells us that, as Earth shrinks, we need a larger and larger velocity to escape. Find the radius of (shrunken) Earth, RB, for which even light cannot escape (this is known as the Schwarzschild radius of Earth). Hint: Compute Rg by using the fact that it occurs exactly when the escape velocity is equal to the speed of light c. Your answer should be an expression in terms of G, ME, and c. (You may find that RB is about 9mm.)
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