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A black hole is an object whose gravitational field is so strong that even light cannot escape from it. To what approximate radius would earth (mass = 5.98 × 10²⁴ kg) have to be compressed to be a black hole?

A

10⁻⁹ m

B

10⁻⁶ m

C

10⁻² m

D

100 m

Step-by-Step Solution

For an object to be a black hole, the escape velocity (vev_e) at its surface must be equal to the speed of light (cc). The formula for escape velocity is ve=2GMRv_e = \sqrt{\frac{2GM}{R}} . To find the radius RR (Schwarzschild radius) where light cannot escape, we set ve=cv_e = c: c=2GMRc2=2GMRR=2GMc2c = \sqrt{\frac{2GM}{R}} \Rightarrow c^2 = \frac{2GM}{R} \Rightarrow R = \frac{2GM}{c^2}. Given: M=5.98×1024M = 5.98 \times 10^{24} kg G6.67×1011 N m2kg2G \approx 6.67 \times 10^{-11} \text{ N m}^2 \text{kg}^{-2} c3×108 m/sc \approx 3 \times 10^8 \text{ m/s} Substituting these values: R=2×(6.67×1011)×(5.98×1024)(3×108)2R = \frac{2 \times (6.67 \times 10^{-11}) \times (5.98 \times 10^{24})}{(3 \times 10^8)^2} R=79.77×10139×10168.86×103 mR = \frac{79.77 \times 10^{13}}{9 \times 10^{16}} \approx 8.86 \times 10^{-3} \text{ m}. This value (8.86 mm8.86 \text{ mm}) is approximately 102 m10^{-2} \text{ m} (10 mm10 \text{ mm}).

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