Work Done By A Force At Right Angles

As explained in NCERT Class 11, Chapter 6 (Work, Energy and Power), the work done by a force is W = F·d·cos(theta), and it vanishes whenever the force is perpendicular to the displacement. In a circular orbit the gravitational force always points toward the centre, while the satellite's velocity and hence its instantaneous displacement are always tangential, so the angle between them is 90 degrees and cos(90) = 0 at every instant. Therefore gravity does zero work throughout, and the satellite's speed and kinetic energy stay constant. The option about positive work equal to kinetic energy contradicts the constancy of speed. The option about negative work mislabels the situation. The option involving speed times circumference ignores the perpendicularity. A consistency check: since the orbital speed is constant, the work-energy theorem demands zero net work, fully agreeing with the geometric argument.