Physics
Grade-10
Easy
Question
A planet in a circular orbit around the Sun moves at a constant speed. The orbit is maintained by the force of gravity between the planet and the Sun. Yet no work is done on the planet. How is it possible?
- No work is done if there is no contact between objects.
- No work is done because there is no gravity in space.
- No work is done if the direction of motion is perpendicular to the force.
- No work is done if objects move in a circle.
Hint:
Work done is given by W = F.S.cos θ
The correct answer is: No work is done if the direction of motion is perpendicular to the force.
We know that work done (W) = F x S x cos θ.
Since the planet moves in a circular orbit, the force of gravity acting on the planet is perpendicular to the direction of motion.
Hence, θ = 90°.
Since, cos 90° = 0, Work done is zero.
Hence, because direction of motion is perpendicular to the force of gravity, no work is done.
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