Question

In elliptical orbit of a planet, as the planet moves from apogee position to perigee position.

Column-I	Column-II
(a) speed of planet	(p) remains same
(b) distance of planet from centre of sun	(q) decreases
(c) potential energy	(r) increases
(d) angular momentum about centre of sun	(s) can not say

• A. (a- p), (b - q), (c - r), (d- s)
• B. (a - s), (b - r), (c - p), (d- q)
• C. (a - r) (b - q), (c - q), (d - p)
• D. None of these

Answer 1

The correct option is C (a - r) (b - q), (c - q), (d - p)

Apogee is the farthest position from focus the planet goes to.
Perigee is the nearest position from focus the planet reaches.

From Kepler's law,

$T^2\propto R^3$

Hence as in this movement from apogee to perigee, R decreases, so T decreases, and hence the speed must increase.

Clearly the distance from focus(Sun) decreases.

Potential energy of system is $-\frac{GMm}{r}$

as 'r' decreases, so does the potential energy(since it is negative).

Angular momentum is conserved since there is no external torque acting on the system of Sun and planet.