1. The problem statement, all variables and given/known data The position vector of a particle is given by r= ihat(2t^3-21t^2+60t+10) +jhat(3/2)(t^2-10t+9) At what time, if any, is the velocity of the particle zero (ie what time is the particle instantaneously at rest) 2. Relevant equations 3. The attempt at a solution Finding the velocity vector is simple, just taking the derivative of position However, when I set that to 0 I have the ihat and the jhat and I don't know how to combine them to solve for the time. Is this even the right step? If I take v= (6t^2-42t+60)ihat+(3t^2-15)jhat and set that to 0 how do I account for the vx and vy when setting that to 0? Do I set vx and vy to 0 separately? I'm really confused. Thanks.