Example:The position of a certain particle is given by: F=2i+19-2r2)万 Find: (1)the trajectory of the particle;(2) position velocity,acceleration of the particle when t=2; (3)when is the velocity perpendicular to the position vector Solution: x=2t,y=19-22 y=19 Example: The position of a certain particle is given by: r ti  t j    2  2  19 2 Find： （1）the trajectory of the particle；（2） position , velocity, acceleration of the particle when t=2； （3）when is the velocity perpendicular to the position vector？ Solution: 2 x  2t , y 19 2t (1) 2 2 1 y 19  x