A photosensitive material is at 9 m to the left of the origin and the source of light is at 7 m to the right of the origin along x-axis. The photosensitive material and the source of light start from rest and move, respectively, with m s-1 and ms-1. The ratio of intensities at t=0 to t=3 s as received by the photosensitive material is
The separation between source and photosensitive material at t:0 is 16 m. Therefore, intensity received by photosensitive material at t=0 is ,where P is the power of source of light.
At t: 3 s, the source is at (15, 0) and detector is at (19, 0), so the separation between them is 4 m.