JEE Advanced 2018 Physics question

In a photoelectric experiment a parallel beam of monochromatic light with power of 200 is incident on a perfectly absorbing cathode of work function 6.25 . The frequency of light is just above the threshold frequency so that the photoelectrons are emitted with negligible kinetic energy. Assume that the photoelectron emission efficiency is 100%. A potential difference of 500 is applied between the cathode and the anode. All the emitted electrons are incident normally on the anode and are absorbed. The anode experiences a force due to the impact of the electrons. The value of is . Mass of the electron and .