An astronomical source emits radio waves with a frequency of 450 MHz. a. If earth is 20 light years from the source, and we measure an intensity of 8.5 x 10-10 W/m2 here on earth, what is the power of the source? b. What is the amplitude of the electric field of the wave at our location?

When a book falls from a shelf to the ground without anyone pushing on it, no work is done on the book. true or false

Using the work energy theorem. what is the velocity of a 850kg car after starting at rest when 13,000j of work is done to it.

When a vertical beam of light passes through a transparent medium, the rate at which its intensity i decreases is proportional to i(t), where t represents the thickness of the medium (in feet). in clear seawater, the intensity 3 feet below the surface is 25% of the initial intensity i0 of the incident beam. what is the intensity of the beam "10" feet below the surface? (give your answer in terms of i0. round any constants or coefficients to five decimal places.)