Question

Does the sun do any work on earth, when earth revolves around the sun in a perfectly circular orbit? Justify the answer.

Answer 1

for a constant force that is not directed along the line, followed by the particle work equals:
A = F*d*cos(θ)
where
θ is the angle between the force vector and the direction of movement;
F - magnitude of force
d - distance
In our case force and direction of motion is perpendicular, so θ=90
Therefore:
cos(90)=0 => A=0 in each moments of time.
Answer: the sun doesn't do any work on earth, when earth revolves around the sun in a perfectly circular orbit.