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7. gravitation — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics7. gravitation1 Mark
MCQ
The condition for a uniform spherical mass $m$ of radius $r$ to be a black hole is [$G=$ gravitational constant and $g=$ acceleration due to gravity]
  • A
    ${(2Gm/r)^{1/2}} \le c$
  • B
    ${(2Gm/r)^{1/2}} = c$
  • ✓
    ${(2Gm/r)^{1/2}} \ge c$
  • D
    ${(gm/r)^{1/2}} \ge c$
✓

Answer

Correct option: C.
${(2Gm/r)^{1/2}} \ge c$
c
(c)Escape velocity for that body ${v_e} = \sqrt {\frac{{2Gm}}{r}} $
${v_e}$ should be more than or equal to speed of light
i.e.$\sqrt {\frac{{2Gm}}{r}} \ge c$

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