An alpha particle collides with an oxygen nucleus, initially at rest. the alpha particle is scattered at an angle of 42.0° above its initial direction of motion, and the oxygen nucleus recoils at an angle of 49.0° below this initial direction. the final speed of the oxygen nucleus is 1.60×10^5 m/s. (the mass of an alpha particle is 4.0 u, and the mass of an oxygen nucleus is 16 u.) what is the final speed of the alpha particle?