please answer the following questions:

Q15. A coherent light ray enters the glass core of an optical fibre from air with refractive index 2.7 at an angle of 35 degrees. Calculate the angle of refraction. (3)Q16. A submarine descends to a depth of 2.8 km. The density of the sea water at the location is 1010 kg/m3. a. Calculate the absolute pressure on the submarine. (4) b. The submarine descends to a new depth where the absolute pressure is one and a half times higher than the absolute pressure in part a. Calculate the new gauge pressure. (3) 0. Calculate the new depth. (2) Q17. A ball of mass 14.0 g and radius 2.50 cm oats half submerged on the surface of a liquid. The buoyant force acting on the ball is equal to 0.137 N. a. Calculate the density of the liquid. (4) b. Explain using a diagram why the ball is able to oat in this liquid. (3)