Question

The moon revolves around the earth because the earth exerts a radial force on the
moon. Does the earth perform work on the moon?
A. no
B. yes, sometimes
C. yes, always
D. cannot be decided

Answer 1

Hint: Gravity is a force of attraction that exists between any two masses, any two bodies, any two particles. Gravity is not just the attraction between objects and the Earth. It is an attraction that exists between all objects, everywhere in the universe. It is an invisible force that pulls objects toward each other. Objects with more mass have more gravity. Gravity also gets weaker with distance. So, the closer objects are to each other, the stronger their gravitational pull is. Earth's gravity comes from all its mass.

Complete step by step answer
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, $W=F\ast s=Fs\cos \theta$ where $\mathrm{\setminus }$ theta is the angle between force an
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, $\theta =90$ hence $\cos \theta =0$
So, $W=|F||s|\ast 0=0$
Hence work done by earth is zero.

Hence the correct answer is option A.

Note: The moon orbits the Earth once every 27.322 days. It also takes approximately 27 days for the moon to rotate once on its axis. As a result, the moon does not seem to be spinning but appears to observers from Earth to be keeping almost perfectly still. The Earth with its moon, as seen from space. The combination of the Moon's size and its distance from the Earth causes the Moon to appear the same size in the sky as the Sun, which is one reason we can have total solar eclipses. It takes the Moon 27.322 days to go around the Earth once.