5. In this question, the vectors i and j and unit vectors cast and north respectively. (a) A particle moves in two dimensions with constant acceleration. Initially it has position vector 3i + 2jm relative to a fixed origin and has initial velocity i + j ms". After 4 seconds it has position vector 7i-4jm. What is its velocity at that time? [4] (b) The particle then continues at constant speed. Calculate how long the particle has been travelling at constant speed when it is southeast of the origin. [4]