Gravity<span> is measured by the acceleration that it gives to freely falling objects. At Earth's surface the acceleration of </span>gravity<span> is about 9.8 metres (32 feet) per second per second.</span>
In the first direct detection of gravitational waves by LIGO in 2015, the waves came from the merger of two black holes. Option B is correct. This is further explained below.
<h3>What are gravitational waves?</h3>
A gravitational wave is simply defined as a ripple in space that is unseen though extremely rapid. Gravitational waves move at light speed. As they pass past, these waves compress and stretch everything in their path.
In conclusion, the merger of two black holes is the first direct detection of gravitational waves.
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Since the Earth is almost spherical in shape, we are actually to find first the volume of the spherical segment at a depth of 1,000 m. The radius of the Earth is 6,371,000 meters. The volume of a spherical segment is:
V = 1/3*πh²(3r - h)
Substituting the values and making sure the units is in mm,
V = 1/3*π(1000 m * 1000 mm/1 m)²[3(6,371,000 m * 1000 mm/1 m) - (1000 m * 1000 mm/1 m)]
V = 2×10²² mm³
Thus, the total amount of bacteria is:
2×10²² mm³ * 100 bacteria/1 mm³ = 2×10²⁴ bacteria