Question

The orbit of Pluto is much more eccentric than the orbits of the other planets. That is, instead of being nearly circular, the orbit is noticeably elliptical. The point in the orbit nearest to the Sun is called the perihelion and the point farthest from the Sun is called the aphelion. As Pluto moves from the perihelion to the aphelion, the work done by gravitational pull of Sun on Pluto is :

• A. zero
• B. positive
• C. negative
• D. depends on sense of rotation

Answer 1

The correct option is C negative

Because the direction of the perihelion to aphelion is opposite to its direction of gravitational pull.

The force exerting on the planet due to the gravity is always toward to sun. When the planet swings from the closest point, perihelion, to the furthest point, aphelion, the effective displacement is away from the sun, not toward it. When the force and its displacement are in opposite direction, the work done by the force is said to be negative.