Question

The escape speed of a projectile on the Earth's surface is 11.2 Kms^-1. A body is projected out with thrice this speed. What is the speed of the body far away from the Earth? Ignore the presence of the Sun and other planets.

Answer 1

If v and v' are the initial and final speeds of the body, its kinetic energies are 1/2 mv² and 1/2mv'² respectively. The initial potential energy of the body (on the earth's surface) = -GMm/R, and the final potential energy (at ∞) = 0

By using the principle of conservation of energy, we get, lnitial K.E. + Initial P.E. = Final K.E. + Final P.E