The escape velocity at the event horizon of a black hole is 3×10^8 m/s, i.e., the velocity of light. What is the mass of the black hole if the distance from its centre to the event horizon is 18km?(a) 12.15 x 10^-30 kg(b) 12.15 x 10^30 kg(c) Infinity(d) Cannot be determinedThe question was posed to me during a job interview.Question is from Gravitation in portion Gravitation of Physics – Class 11

The escape velocity at the event horizon of a black hole is 3×10^8 m/

1.	The escape velocity at the event horizon of a black hole is 3×10^8 m/s, i.e., the velocity of light. What is the mass of the black hole if the distance from its centre to the event horizon is 18km?(a) 12.15 x 10^-30 kg(b) 12.15 x 10^30 kg(c) Infinity(d) Cannot be determinedThe question was posed to me during a job interview.Question is from Gravitation in portion Gravitation of Physics – Class 11
Answer» Correct CHOICE is (b) 12.15 x 10^30 kg Best explanation: ESCAPE velocity (v) = [(2 x G x M)/R] ^1/2 M = Mass of the black hole R = Radius of the black hole 3 x 10^8 = [(2 x 6.67 x 10^-11 x M)/18000]^1/2 9 x 10^16 = (2 x 6.67 x 10^-11 x M)/18000 M = 12.15 x 10^30kg.

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