1.

A body of mass 20 kg is at rest on the earth’s surface,(i) Find its gravitational potential energy,(ii) Find the kinetic energy to be provided to the body to make it free from the gravitational influence of the earth.(g = 9.8 m/s2, R = 6400 km)

Answer»

Data : m = 20 kg, g = 9.8 m/s2,

R = 6400 km = 6.4 × 106 m

(i) The gravitational potential energy of the body = \(-\frac{GMm}{R}=-mgR\)

\((\because\,g=\frac{GM}{R^2})\)

= – 20 kg × 9.8 m/s2 × 6.4 × 106 m

= – 1.2544 × 109 J.

(ii) To make the body free from the gravitational influence of the earth, it should be provided kinetic energy equal to 1.2544 × 109 J.



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