<span>Velocities are vectors so we can add them!
Let's let +x be East and -x be West.
-0.9 + 2.7 = 1.8
Since our answer is positive that means East so the answer is C.</span>
Answer:
η = 1.31
Explanation:
The formula for the refractive index of from air to some other medium is given by the following formula:

where,
η = refractive index = ?
c = speed of light in air = 3 x 10⁸ m/s
v = speed of light in ice = 2.29 x 10⁸ m/s
Therefore, using these values in the equation we get:

<u>η = 1.31</u>
A. 
The orbital speed of the clumps of matter around the black hole is equal to the ratio between the circumference of the orbit and the period of revolution:

where we have:
is the orbital speed
r is the orbital radius
is the orbital period
Solving for r, we find the distance of the clumps of matter from the centre of the black hole:

B. 
The gravitational force between the black hole and the clumps of matter provides the centripetal force that keeps the matter in circular motion:

where
m is the mass of the clumps of matter
G is the gravitational constant
M is the mass of the black hole
Solving the formula for M, we find the mass of the black hole:

and considering the value of the solar mass

the mass of the black hole as a multiple of our sun's mass is

C. 
The radius of the event horizon is equal to the Schwarzschild radius of the black hole, which is given by

where M is the mass of the black hole and c is the speed of light.
Substituting numbers into the formula, we find
