Mass of the Earth = 5.972 x 10²⁴ kg
Mass of the asteroid = 1 x 10⁹ kg
Separation distance = 3 x 10⁶ m (between the Earth's center and the asteroid's center)
Gravitational force between two masses =
(6.67 x 10⁻¹¹ nt-m²/kg²) · m₁ · m₂ / (distance)²
= (6.67 x 10⁻¹¹ nt-m²/kg²) · (5.972 x 10²⁴ kg) · (1 x 10⁹ kg) / (3 x 10⁶ m)²
= (6.67 · 5.972 / 9) x 10¹⁰ · (nt · m² · kg · kg / kg² · m²)
= 13.28 x 10¹⁰ newtons
= 132.8 Giga-newtons .
(about 14,926,763 tons)