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Work, Energy, and Power — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsWork, Energy, and Power1 Mark
MCQ
The moon revolves around the earth because the earth exerts a radial force on the moon. Does the earth perform work on the moon?
  • ✓
    No
  • B
    yes, sometimes
  • C
    yes, always
  • D
    cannot be decided
✓

Answer

Correct option: A.
No
No, the earth does not perform any work on the moon.
Work done$(W)$ is defined as the scalar product of force$(F)$ and displacement$(s).$
So, $W = F \times s = Fs\cos I$ where is the angle between force and displacement vector.
The radial force exerted on the moon by earth i.e attractive force due to gravity acts in direction perpendicular to which the moon suffers the displacement during rotation.
So, $I = 90$ hence $\cos I = 0$
So, $W = |F|| s| \times 0 = 0$

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