1. The problem statement, all variables and given/known data The coordinates of the particle is given by: x(t)=(1.2 m/s)t y(t)=15m-(0.5m/s2)t2 a) At what times is the particle's velocity perpendicular to its acceleration b) At what times is the particle's speed instantaneously not changing (I get that the acceleration is zero). c) At what times is the particle's position perpendicular to its velocity. d) What is the particle's minimum distance from the origin. 2. Relevant equations r=xi+yj (i and j are the corresponding unit vectors) vx=dx/dt vy=dy/dt a=dv/dt. 3. The attempt at a solution I tried to differentiate the particle position r with respect to time getting velocity, and then taking the derivative of the velocity with respect to time getting acceleration. When I had the acceleration as function of time, I got: a=(-2*0.5 m/s2)j. But how can I then solve for t, when it is not in the equation? What have I done wrong? Please help me with all the questions.