In the gure, projectile particle 1 is an alpha particle and target particle 2 is an oxygen nucleus. The alpha particle is scattered at angle 91 = 61.3 and the oxygen nucleus recoils with speed 1.00 X 105 m/s and at angle 92 = 53.0. |n atomic mass units, the mass of the alpha particle is 4.00 u and the mass ofthe oxygen nucleus is 16.0 u. What are the (a) nal and (b) initial speeds of the alpha particle? (a) Number n? l Units m/s v (b) Number a? n Units m/s V eTextbook and Media Assistance Used m Assistance Used The net external force on the two particle system is zero; thus, the net momentum of the system cannot change. The net momentum along the x axis before the collision must equal that after the collision. Same for the y axis. Key Ideas I lftwo bodies collide and their motion is not along a single axis (the collision is not head-on), the collision is two-dimensional. lfthe two-body system is closed and isolated, the law of conservation of momentum applies to the collision and can be written as 11+ 32f = u + 32):. In component form, the law gives two equations that describe the collision (one equation for each of the two dimensions]. Ifthe collision is also elastic (a special case), the conservation ofkinetic energy during the collision gives a third equation: K11+K2[: K1f+K2f