1. The problem statement, all variables and given/known data A foreign fishing submarine moves straight north through Canadian waters at a constant velocity of 12 m/s and a constant depth of 150m below the surface. A Canadian helicopter is in pursuit, flying in exactly the same direction at a constant velocity of 52 m/s and a constant altitude of 550m above the surface. The helicopter, lightly armed, shoots a narrow laser beam which enters the water and strikes the submarine. At one instant, the laser beam leaving the helicopter is directed at an angle of 10° below the horizontal to hit the target. At a later time, the beam has to be tilted down to 30° below the horizontal to maintain contact. Given that the index of refraction is 1.00 for air and 1.33 for water, find the time interval between the above events. Possible Answers; a) 33.3 b) 55.1 c) 68.9 d) 46.7 e) 78 2. Relevant equations n1xsin∅1 = n2xsin∅2 3. The attempt at a solution I found the two refractive angles; 1xsin10° = 1.33xsin∅1 ∅1 = 7.5° 1xsin30° = 1.33xsin∅2 ∅2 = 22.08° After that, I'm stuck. I have no idea how to use that to find the time interval between each degree.