1. The problem statement, all variables and given/known data A particle p traveling with a speed of vpi = 3 m/s hits and scatters elastically from another particle N, initially at rest. Particle p is deflected through 90°, leaving with a speed of vpf = 2.3 m/s, and a mass mp = 2 kg. a) What angle (in degrees) does the recoiling N make to the incident-p direction? b) What is the magnitude of the momentum of the recoiling N? c) What is the change in the energy of the p? d) What is the speed of the recoiling N? e) What is the mass of the N? 2. Relevant equations mv=p mpv0p + mNv0N=mpvfp + mNvfN (for x and y directions) 3. The attempt at a solution a) Since N is at rest at first, and p is perpendicular to the x-axis after the collision, I assumed that the pfNx would equal the initial momentum of p, or 2kg*3m/s or 5kg*m/s. For the y direction, the momentum of N has to be equal and opposite p's momentum, so it is = -4.6kg*m/s. I used inverse tangent to get the angle = -47.4 which is wrong. Where did I go wrong? b) c) d) e) I have c) and I am sure I know how to do the rest if I can get a) right. Thanks.