Question

As Pluto moves from the perihelion to the aphelion, the work done by the gravitational pull of the Sun on Pluto is

(A) is zero
(B) is positive
(C) is negative
(D) depends on sense or rotation

Answer 1

Hint: Gravitational pull is maximum when the gravitational attraction object and the other is close. Pluto rotates around the sun in the orbit. The orbit of Pluto is eccentric in shape. Gravitational pull decreases when the distance between the points of gravitation increases.

Complete step by step answer:
Perihelion is the shortest point in the orbit of space bodies from the sun. Aphelion is the farthest point in the orbit from the sun. The gravitational pull of the sun to Pluto is always towards the center of the sun. Hence, at the point of perihelion, Pluto is closest to the sun. At this point, the gravitational pull is maximum. When Pluto is at the aphelion, the work done by the gravitational pull is minimum. This is because at the point of aphelion, Pluto is at the longest distance from the sun and hence the work done by the gravitational pull decreases for some distance, at some point the work done by the gravitational pull will become zero, and still the distance increases, work done by the gravitational pull goes to negative.

Thus, option (C) is correct.

Additional information:
Pluto was discovered in 1930 by Clyde Tombaugh. Once Pluto is one of the planets and distant from the sun. But it does not meet the criteria of the planet and hence now it is considered as the largest dwarf planet and biggest known member of the Kuiper belt.

Note:
The orbit of Pluto is more eccentric than the orbit of the other planets. So, the gravitational pull by the sun on Pluto is maximum when Pluto is close to the sun and the gravitational pull by the sun on Pluto is minimum when Pluto is far away from the sun.