1. The problem statement, all variables and given/known data A particle A of mass m is travelling on a horizontal surface with velocity 7i-4j and collides with a stationary particle of mass 3m at the origin of the co-ordinate system at time t=0 Find an expression for the position vector of A at time t<0 NB: There is more to this question but this is the part I don't understand. The question itself is confusing to me. 2. Relevant equations 3. The attempt at a solution I integrate the velocity, a constant, so taking the velocity of A as v I integrate and get vt + C So: converting back to component form I get 7ti-4tj but still with the '+ C' Clearly this cant be right. If you can point me in the right direction I'd appreciate it.