According to the universal law of gravitation, gravitational force exerted on an object of mass m is given by

= / ^{2 }

Where,

Mass of Earth, M = 6 × 10^{24} kg

Mass of object, m = 1 kg

Universal gravitational constant, G = 6.7 × 10^{−11} Nm^{2} kg^{−2 }

Since the object is on the surface of the Earth,

r = radius of the Earth (R)

r = R = 6.4 × 10^{6} m

Therefore, the gravitational force

= / 2 = 6.7 × 10^{−11} × 6 × 10^{24} × 1 / (6.4 × 106) 2 = 9.8