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Q.
The earth moves in an elliptical orbit with the sun S at one of foci as shown in the figure. Its rotational kinetic energy is maximum at the point
Gravitation
Solution:
The earth revolves around the sun once in a year. In order to find the rotational kinetic energy about the sun, we may treat the earth as a point mass, of moment of inertia I. If $\omega$ is angular velocity of earth, then
$ K_{rot} = \frac{1}{2} I \omega^2$
In planetary motion, angular momentum remains conserved.
At A, the moment of inertia is least, so angular speed is maximum. So, at A, rotational kinetic energy is maximum.
