Question

What will be the change in the following energies
i) Kinetic ii) Potential iii) Mechanical, if a body enters into earth atmosphere from infinity.

Answer 1

Let us think it in a practical way where the resistances are negelcted. When a body fall from infinity, where it is assumed to be at rest, to the earth it is same like that of free falling and as this is the case of falling an object from the space it will travel with the escape velocity ie 11/s. So considering the object initially at rest and when the body enters into the atmosphere it has a velocity of 11km/s=11,000m/s. Therefore change in KE= (1/2)m((11,000m/s)^2). As the body was at rest the potential energy was converted to kinetic energy. And the mechanical energy is the sum of both potential and kinetic.