question_answer 35)

                  If the law of gravitation, instead of being inverse-square law, becomes an inverse-cube law-                      (a) planers will not have elliptic orbits.                 (b) circular orbits of planets is not possible                 (c) projectile motion of a stone thrown by hand on the surface of the earth will be approximately parabolic.                                (d) there will be no gravitational force inside a spherical shell of uniform density.

Answer:

                  (a, c) If \[F=\frac{K}{{{r}^{n}}},\] orbits are stable for \[n<3\].                 The orbits are unstable if \[n\ge 3\].