The net force on the hanging object is zero. If it were not zero, then the object would be accelerating in some direction.
Frequency decreases whilst wavelength increases and the opposite also occurs
The gravitational force is inversely proportional to the
square of the distance between their centers. So the
force is greatest when the distance is zero.
M=2.45 because you multiply out the equation on the right and divide by 10
No work is done because the object needs to be moved. The formula for work is Work = Force x Distance.