Position and acceleration vector -- parallel and perpendicular 1. The problem statement, all variables and given/known data The motion of a particle is defined by the position vector r = A(Cos t + t Sin t) i + A(Sin t + t Cos t) j where t is expressed in seconds. Determine the values of t for which the position vector and acceleration vector are a) perpendicular b) parallel 2. Relevant equations 3. The attempt at a solution For acceleration i have differentiate r twice and arrive at the equation. So, i should go for cross product to find 't' when they are parallel and dot product when they are perpendicular. Am I right in my procedure, revered members?