Let's convert first the wavelength into meters:

Then, we know that the wavelength is related to the frequency by the following equation:

Where

is the speed of light in free space. Therefore, putting in the numbers, we find the frequency f:
Answer:
15.625 watts
Explanation:
Recall that power is defined as the worked performed per unit of time:
Power = Work / time
The work done is Force * distance, so in our case the work is:
Work = 25 M * 5 m = 125 J
Then the power will be:
Power = 125 J / 8 sec = 15.625 watts
The radius of the sphere is r=5.15 cm=0.0515 m, and its surface is given by

So the total charge on the surface of the sphere is, using the charge density

:

The electrostatic force between the sphere and the point charge is:

where
ke is the Coulomb's constant
Q is the charge on the sphere

is the point charge
r is their separation
Re-arranging the equation, we can find the separation between the sphere and the point charge: