26. Figure shows a roller coaster car at rest on the track at the top of a hill that is 15 m high. The car has a mass of 10.0 kg. It begins to move and reaches a speed of 10.0 m/s at the top of the second hill, point A, on the track. Calculate the height of hill A. 15 m (2 marks) 27. A light with wavelength, 450 nm, falls on a diffraction grating (multiple slits). On a screen 1.80 m away the distance between dark fringes on either side of the bright central is 4.20 mm. a. What is the separation between a set of slits? b. How many lines per meter are on the grating? (4 marks)